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Critical points in zero-one laws for

G(n, p)

Maksim Zhukovskii
MSU, MIPT, Yandex

Workshop on random graphs and their applications
26 October 2013

1/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
First-order properties.

First-order formulae:
relational symbols ∼, =;
logical connectivities ¬, ⇒, ⇔, ∨, ∧;
variables x, y, x1, ...;
quantiers ∀, ∃.

2/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
First-order properties.

First-order formulae:
relational symbols ∼, =;
logical connectivities ¬, ⇒, ⇔, ∨, ∧;
variables x, y, x1, ...;
quantiers ∀, ∃.
• property of a graph to be complete
∀x ∀y (¬(x = y) ⇒ (x ∼ y)).

2/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
First-order properties.

First-order formulae:
relational symbols ∼, =;
logical connectivities ¬, ⇒, ⇔, ∨, ∧;
variables x, y, x1, ...;
quantiers ∀, ∃.
• property of a graph to be complete
∀x ∀y (¬(x = y) ⇒ (x ∼ y)).
•

property of a graph to contain a triangle
∃x ∃y ∃z ((x ∼ y) ∧ (y ∼ z) ∧ (x ∼ z)).

2/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
First-order properties.

First-order formulae:
relational symbols ∼, =;
logical connectivities ¬, ⇒, ⇔, ∨, ∧;
variables x, y, x1, ...;
quantiers ∀, ∃.
• property of a graph to be complete
∀x ∀y (¬(x = y) ⇒ (x ∼ y)).
•

property of a graph to contain a triangle
∃x ∃y ∃z ((x ∼ y) ∧ (y ∼ z) ∧ (x ∼ z)).

•
2/17

property of a graph to have chromatic number k
Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Limit probabilities.
G(n, p): n

probability

3/17

 number of vertices, p  edge appearance

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Limit probabilities.
G(n, p): n

 number of vertices, p  edge appearance

probability
G  an arbitrary graph, LG  property of containing G.

3/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Limit probabilities.
G(n, p): n

 number of vertices, p  edge appearance

probability
G  an arbitrary graph, LG  property of containing G.
LG is the rst order property.

3/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Limit probabilities.
G(n, p): n

 number of vertices, p  edge appearance

probability
G  an arbitrary graph, LG  property of containing G.
LG is the rst order property.
e(H)
maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) ,
p0 = n−1/ρ (G) ;
max

3/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Limit probabilities.
G(n, p): n

 number of vertices, p  edge appearance

probability
G  an arbitrary graph, LG  property of containing G.
LG is the rst order property.
e(H)
maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) ,
p0 = n−1/ρ (G) ;
max

p

p0 ⇒ lim Pn,p (LG ) = 1,

p

p0 ⇒ lim Pn,p (LG ) = 0,

n→∞

n→∞

p=p0 ⇒ lim Pn,p (LG )∈ {0, 1}.
/
n→∞

3/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Limit probabilities.
G(n, p): n

 number of vertices, p  edge appearance

probability
G  an arbitrary graph, LG  property of containing G.
LG is the rst order property.
e(H)
maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) ,
p0 = n−1/ρ (G) ;
max

p

p0 ⇒ lim Pn,p (LG ) = 1,

p

p0 ⇒ lim Pn,p (LG ) = 0,

n→∞

n→∞

p=p0 ⇒ lim Pn,p (LG )∈ {0, 1}.
/
n→∞

If G  set of graphs, L = {LG, LG, G ∈ G},
p = n−α , α is irrational
3/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Limit probabilities.
G(n, p): n

 number of vertices, p  edge appearance

probability
G  an arbitrary graph, LG  property of containing G.
LG is the rst order property.
e(H)
maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) ,
p0 = n−1/ρ (G) ;
max

p

p0 ⇒ lim Pn,p (LG ) = 1,

p

p0 ⇒ lim Pn,p (LG ) = 0,

n→∞

n→∞

p=p0 ⇒ lim Pn,p (LG )∈ {0, 1}.
/
n→∞

If G  set of graphs, L = {LG, LG, G ∈ G},
p = n−α , α is irrational
then ∀L ∈ L limn→∞ Pn,p(L) ∈ {0, 1}.
3/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Zero-one law
L

 the set of all rst-order properties.

Denition
The random graph obeys zero-one law if ∀L ∈ L
lim Pn,p(n) (L) ∈ {0, 1}.

n→∞

P

4/17

is a set of functions p such that G(n, p) obeys zero-one law.

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Zero-one law
L

 the set of all rst-order properties.

Denition
The random graph obeys zero-one law if ∀L ∈ L
lim Pn,p(n) (L) ∈ {0, 1}.

n→∞

P

is a set of functions p such that G(n, p) obeys zero-one law.

Theorem [J.H. Spencer, S. Shelah, 1988]
Let p = n−α, α ∈ (0, 1].
If α ∈ R  Q then p ∈ P .
If α ∈ Q then p ∈ P .
/
4/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Quantier depth.
Quantier depths of x = y, x ∼ y equal 0.

5/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Quantier depth.
Quantier depths of x = y, x ∼ y equal 0.
If quantier depth of φ equals k then quantier depth of ¬φ
equals k as well.

5/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Quantier depth.
Quantier depths of x = y, x ∼ y equal 0.
If quantier depth of φ equals k then quantier depth of ¬φ
equals k as well.
If quantier depth of φ1 equals k1, quantier depth of φ2 equals
then quantier depths of φ1 ⇒ φ2, φ1 ⇔ φ2, φ1 ∨ φ2,
equal max{k1, k2}.

k2
φ1 ∧ φ2

5/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Quantier depth.
Quantier depths of x = y, x ∼ y equal 0.
If quantier depth of φ equals k then quantier depth of ¬φ
equals k as well.
If quantier depth of φ1 equals k1, quantier depth of φ2 equals
then quantier depths of φ1 ⇒ φ2, φ1 ⇔ φ2, φ1 ∨ φ2,
equal max{k1, k2}.

k2
φ1 ∧ φ2

If quantier depth of φ(x) equals k, then quantier depths of
∃x φ(x), ∀x φ(x) equal k + 1.

5/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Bounded quantier depth.
 the class of rst-order properties dened by formulae with
quantier depth bounded by k.
Random graph G(n, p) obeys zero-one k-law if ∀L ∈ Lk
Lk

lim Pn,p(n) (L) ∈ {0, 1}.

N →∞

 the class of all functions p = p(n) such that random graph
obeys zero-one k-law.

Pk
G(n, p)

6/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Bounded quantier depth.
 the class of rst-order properties dened by formulae with
quantier depth bounded by k.
Random graph G(n, p) obeys zero-one k-law if ∀L ∈ Lk
Lk

lim Pn,p(n) (L) ∈ {0, 1}.

N →∞

 the class of all functions p = p(n) such that random graph
obeys zero-one k-law.

Pk
G(n, p)

Example:

6/17

(∀x ∃y (x ∼ y)) ∧ (∀x ∃y ¬(x ∼ y))
∀x ∃y ∃z ((x ∼ y) ∧ (¬(x ∼ z)))

Maksim Zhukovskii

k=2
k=3

Critical points in zero-one laws for

G(n, p)
Zero-one k-laws
Zhukovskii; 2010 (zero-one
Let

p=n
If

7/17

−α

k -law)

, k ∈ N, k ≥ 3.

0α

1
k−2 then

p ∈ Pk .

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Zero-one k-laws
Zhukovskii; 2010 (zero-one
Let

p=n
If

−α

k -law)

, k ∈ N, k ≥ 3.

0α

1
k−2 then

p ∈ Pk .

Zhukovskii; 2012+ (extension of zero-one
Let

p=n
If

7/17

−α

, k ∈ N, k ≥ 4, Q =

α=1−

1
,
2k−1 +β

{a,
b

a, b ∈ N, a ≤ 2k−1 }

β ∈ (0, ∞)  Q

Maksim Zhukovskii

k -law)

then

p ∈ Pk .

Critical points in zero-one laws for

G(n, p)
Zero-one k-laws
Zhukovskii; 2010 (zero-one
Let

p=n
If

−α

k -law)

, k ∈ N, k ≥ 3.

0α

1
k−2 then

p ∈ Pk .

Zhukovskii; 2012+ (extension of zero-one
Let

p=n
If

−α

, k ∈ N, k ≥ 4, Q =

α=1−

1
,
2k−1 +β

1−
1−

...

1
,1
2k

1−

1


1 −

k−1
2k−1 − 2 3
2

then

p ∈ Pk .

1
1
,1 − k
2k − 1
2

,1 −

Maksim Zhukovskii

k -law)

a, b ∈ N, a ≤ 2k−1 }

β ∈ (0, ∞)  Q

1
1
, 1 − k−1
2k−1 + 2k−2
2
+ 2k−2 + 1


2k−1 +
7/17

{a,
b

1−

...
1

2k−1

+

2k−1 −1
2

,1 −

1
2k−1 + 2k−2


1
2k−1 +

2k−1
3




. . .? . . .

0,

1
k−2

Critical points in zero-one laws for

.

G(n, p)
Zero-one k-laws
Zhukovskii; 2013++ (no
Let

p=n

−α

k -law)

, k ∈ N.

If

k ≥ 3, α =

If

1
k−2

k ≥ 4,

then

˜
Q=

 k−1
 2
 k−1 − 2 · 1, . . . , 1;

 2
−2·1−1·2
,..., 1;
2
2
 2k−1 −2·1−3·2−1·3 , . . . ;


5

...;

α=1−

8/17

p ∈ Pk .
/

1
,
2k−1 +β

˜
β∈Q

2

k−1

−2·1−2·2
1
,..., 3;
3

...;
...;
then

k−1

−2·1−3·2
,..., 1;
4
4
2k−1 −2·1−3·2−4·3
,...;
8

2

...











p ∈ Pk .
/

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

9/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

9/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

9/17

1
2k

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

9/17

1
2k

1
2k −1

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

9/17

1
2k

1
2k −1

1
2k −2

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

9/17

1
2k

1
2k −1

1
2k −2

1
2k −3

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

9/17

1
2k

1
2k −1

1
2k −2

1
2k −3

...

Maksim Zhukovskii

1
2k −2k−2

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

9/17

1
2k

1
2k −1

1
2k −2

1
2k −3

...

Maksim Zhukovskii

1
2k −2k−2

...

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

1
2k

1
2k −1

Large gap:

9/17

1
2k −2

1
2k −3

...

1
2k −2k−2

...

?

[1/2k−1 , 1 − 1/(k − 2))

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0

1
2k

1
2k −1

Large gap:

9/17

1
2k −2

1
2k −3

...

1
2k −2k−2

...

?

1−

1
k−2

[1/2k−1 , 1 − 1/(k − 2))

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Critical points

1−α: 0→1

0
Large gap:

9/17

1
2k −2

1
2k −3

...

1
2k −2k−2

...

?

1−

1
k−2

[1/2k−1 , 1 − 1/(k − 2))

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Intervals

10/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht game
EHR(G, H, k)
 two graphs
k  number of rounds
Spoiler  Duplicator  two players
G, H

11/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht theorem
Theorem [A. Ehrenfeucht, 1960]
Let G, H be two graphs. For any rst-order property L expressed
by formula with quantier depth bounded by a number k
G ∈ L ⇔ H ∈ L if and only if Duplicator has a winning strategy in
the game EHR(G, H, k).
Example: ∃x1 ∃x2 ∃x3 ((x1 ∼ x2) ∧ (x2 ∼ x3) ∧ (x1 ∼ x3)).

12/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht theorem
Theorem [A. Ehrenfeucht, 1960]
Let G, H be two graphs. For any rst-order property L expressed
by formula with quantier depth bounded by a number k
G ∈ L ⇔ H ∈ L if and only if Duplicator has a winning strategy in
the game EHR(G, H, k).
Example: ∃x1 ∃x2 ∃x3 ((x1 ∼ x2) ∧ (x2 ∼ x3) ∧ (x1 ∼ x3)).

12/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Ehrenfeucht theorem
Theorem [A. Ehrenfeucht, 1960]
Let G, H be two graphs. For any rst-order property L expressed
by formula with quantier depth bounded by a number k
G ∈ L ⇔ H ∈ L if and only if Duplicator has a winning strategy in
the game EHR(G, H, k).
Example: ∃x1 ∃x2 ∃x3 ((x1 ∼ x2) ∧ (x2 ∼ x3) ∧ (x1 ∼ x3)).

12/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Proofs of k-laws

Corollary
Zero-one law holds if and only if for any k ∈ N almost surely
Duplicator has a winning strategy in the Ehrenfeucht game on
k rounds.
Random graph G(n, p) obeys zero-one k-law if and only if
almost surely Duplicator has a winning strategy in the
Ehrenfeucht game on k rounds.

13/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Case k = 4, α = 13/14

14/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Case k = 4, α = 13/14
FISH GRAPH

,

,

e = 14 v = 13 ρ = 14/13

14/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Case k = 4, α = 13/14
FISH GRAPH

,
,
G(n, n−13/14 ) contains a copy of FISH GRAPH with positive
asymptotical probability;
G(n, n−13/14 ) does not contain a copy of any graph with at most
13 vertices and maximal density at least 14/13 with positive
asymptotical probability.
e = 14 v = 13 ρ = 14/13

14/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Case k = 4, α = 13/14
FISH GRAPH

,
,
G(n, n−13/14 ) contains a copy of FISH GRAPH with positive
asymptotical probability;
G(n, n−13/14 ) does not contain a copy of any graph with at most
13 vertices and maximal density at least 14/13 with positive
asymptotical probability.
EHR(G, H, 4):
e = 14 v = 13 ρ = 14/13

14/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Case k = 4, α = 13/14
FISH GRAPH

,
,
G(n, n−13/14 ) contains a copy of FISH GRAPH with positive
asymptotical probability;
G(n, n−13/14 ) does not contain a copy of any graph with at most
13 vertices and maximal density at least 14/13 with positive
asymptotical probability.
EHR(G, H, 4):
G contains FISH GRAPH;
e = 14 v = 13 ρ = 14/13

14/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Case k = 4, α = 13/14
FISH GRAPH

,
,
G(n, n−13/14 ) contains a copy of FISH GRAPH with positive
asymptotical probability;
G(n, n−13/14 ) does not contain a copy of any graph with at most
13 vertices and maximal density at least 14/13 with positive
asymptotical probability.
EHR(G, H, 4):
G contains FISH GRAPH;
H does not contain a copy of any graph with at most 13
vertices and maximal density at least 14/13.
e = 14 v = 13 ρ = 14/13

14/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Winning strategy of Spoiler

15/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Open questions
What happens when α ∈

16/17

1
k−2 , 1

Maksim Zhukovskii

−

1
2k−1

?

Critical points in zero-one laws for

G(n, p)
Open questions
What happens when α ∈

1
k−2 , 1

−

1
2k−1

?

Spencer and Shelah, 1988: There exists a rst-order property and
an innite set S of rational numbers from (0, 1) such that for any
α ∈ S random graph G(n, n−α ) follows the property with
probability which doesn't tend to 0 or to 1.

16/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Open questions
What happens when α ∈

1
k−2 , 1

−

1
2k−1

?

Spencer and Shelah, 1988: There exists a rst-order property and
an innite set S of rational numbers from (0, 1) such that for any
α ∈ S random graph G(n, n−α ) follows the property with
probability which doesn't tend to 0 or to 1.
For any xed k and any ε  0 in 1 − 2 1 + ε, 1 there is only
nite number of critical points. Does this property holds for
1 − 2 1 , 1 ? Are there any other such subintervals in
1
1
?
k−2 , 1 − 2
k−1

k−1

k−1

16/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)
Thank you!

Thank you very much for your
attention!

17/17

Maksim Zhukovskii

Critical points in zero-one laws for

G(n, p)

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3 zhukovsky

  • 1. Critical points in zero-one laws for G(n, p) Maksim Zhukovskii MSU, MIPT, Yandex Workshop on random graphs and their applications 26 October 2013 1/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 2. First-order properties. First-order formulae: relational symbols ∼, =; logical connectivities ¬, ⇒, ⇔, ∨, ∧; variables x, y, x1, ...; quantiers ∀, ∃. 2/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 3. First-order properties. First-order formulae: relational symbols ∼, =; logical connectivities ¬, ⇒, ⇔, ∨, ∧; variables x, y, x1, ...; quantiers ∀, ∃. • property of a graph to be complete ∀x ∀y (¬(x = y) ⇒ (x ∼ y)). 2/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 4. First-order properties. First-order formulae: relational symbols ∼, =; logical connectivities ¬, ⇒, ⇔, ∨, ∧; variables x, y, x1, ...; quantiers ∀, ∃. • property of a graph to be complete ∀x ∀y (¬(x = y) ⇒ (x ∼ y)). • property of a graph to contain a triangle ∃x ∃y ∃z ((x ∼ y) ∧ (y ∼ z) ∧ (x ∼ z)). 2/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 5. First-order properties. First-order formulae: relational symbols ∼, =; logical connectivities ¬, ⇒, ⇔, ∨, ∧; variables x, y, x1, ...; quantiers ∀, ∃. • property of a graph to be complete ∀x ∀y (¬(x = y) ⇒ (x ∼ y)). • property of a graph to contain a triangle ∃x ∃y ∃z ((x ∼ y) ∧ (y ∼ z) ∧ (x ∼ z)). • 2/17 property of a graph to have chromatic number k Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 6. Limit probabilities. G(n, p): n probability 3/17 number of vertices, p edge appearance Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 7. Limit probabilities. G(n, p): n number of vertices, p edge appearance probability G an arbitrary graph, LG property of containing G. 3/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 8. Limit probabilities. G(n, p): n number of vertices, p edge appearance probability G an arbitrary graph, LG property of containing G. LG is the rst order property. 3/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 9. Limit probabilities. G(n, p): n number of vertices, p edge appearance probability G an arbitrary graph, LG property of containing G. LG is the rst order property. e(H) maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) , p0 = n−1/ρ (G) ; max 3/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 10. Limit probabilities. G(n, p): n number of vertices, p edge appearance probability G an arbitrary graph, LG property of containing G. LG is the rst order property. e(H) maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) , p0 = n−1/ρ (G) ; max p p0 ⇒ lim Pn,p (LG ) = 1, p p0 ⇒ lim Pn,p (LG ) = 0, n→∞ n→∞ p=p0 ⇒ lim Pn,p (LG )∈ {0, 1}. / n→∞ 3/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 11. Limit probabilities. G(n, p): n number of vertices, p edge appearance probability G an arbitrary graph, LG property of containing G. LG is the rst order property. e(H) maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) , p0 = n−1/ρ (G) ; max p p0 ⇒ lim Pn,p (LG ) = 1, p p0 ⇒ lim Pn,p (LG ) = 0, n→∞ n→∞ p=p0 ⇒ lim Pn,p (LG )∈ {0, 1}. / n→∞ If G set of graphs, L = {LG, LG, G ∈ G}, p = n−α , α is irrational 3/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 12. Limit probabilities. G(n, p): n number of vertices, p edge appearance probability G an arbitrary graph, LG property of containing G. LG is the rst order property. e(H) maximal density ρmax(G) = maxH⊆G{ρ(H)}, ρ(H) = v(H) , p0 = n−1/ρ (G) ; max p p0 ⇒ lim Pn,p (LG ) = 1, p p0 ⇒ lim Pn,p (LG ) = 0, n→∞ n→∞ p=p0 ⇒ lim Pn,p (LG )∈ {0, 1}. / n→∞ If G set of graphs, L = {LG, LG, G ∈ G}, p = n−α , α is irrational then ∀L ∈ L limn→∞ Pn,p(L) ∈ {0, 1}. 3/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 13. Zero-one law L the set of all rst-order properties. Denition The random graph obeys zero-one law if ∀L ∈ L lim Pn,p(n) (L) ∈ {0, 1}. n→∞ P 4/17 is a set of functions p such that G(n, p) obeys zero-one law. Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 14. Zero-one law L the set of all rst-order properties. Denition The random graph obeys zero-one law if ∀L ∈ L lim Pn,p(n) (L) ∈ {0, 1}. n→∞ P is a set of functions p such that G(n, p) obeys zero-one law. Theorem [J.H. Spencer, S. Shelah, 1988] Let p = n−α, α ∈ (0, 1]. If α ∈ R Q then p ∈ P . If α ∈ Q then p ∈ P . / 4/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 15. Quantier depth. Quantier depths of x = y, x ∼ y equal 0. 5/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 16. Quantier depth. Quantier depths of x = y, x ∼ y equal 0. If quantier depth of φ equals k then quantier depth of ¬φ equals k as well. 5/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 17. Quantier depth. Quantier depths of x = y, x ∼ y equal 0. If quantier depth of φ equals k then quantier depth of ¬φ equals k as well. If quantier depth of φ1 equals k1, quantier depth of φ2 equals then quantier depths of φ1 ⇒ φ2, φ1 ⇔ φ2, φ1 ∨ φ2, equal max{k1, k2}. k2 φ1 ∧ φ2 5/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 18. Quantier depth. Quantier depths of x = y, x ∼ y equal 0. If quantier depth of φ equals k then quantier depth of ¬φ equals k as well. If quantier depth of φ1 equals k1, quantier depth of φ2 equals then quantier depths of φ1 ⇒ φ2, φ1 ⇔ φ2, φ1 ∨ φ2, equal max{k1, k2}. k2 φ1 ∧ φ2 If quantier depth of φ(x) equals k, then quantier depths of ∃x φ(x), ∀x φ(x) equal k + 1. 5/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 19. Bounded quantier depth. the class of rst-order properties dened by formulae with quantier depth bounded by k. Random graph G(n, p) obeys zero-one k-law if ∀L ∈ Lk Lk lim Pn,p(n) (L) ∈ {0, 1}. N →∞ the class of all functions p = p(n) such that random graph obeys zero-one k-law. Pk G(n, p) 6/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 20. Bounded quantier depth. the class of rst-order properties dened by formulae with quantier depth bounded by k. Random graph G(n, p) obeys zero-one k-law if ∀L ∈ Lk Lk lim Pn,p(n) (L) ∈ {0, 1}. N →∞ the class of all functions p = p(n) such that random graph obeys zero-one k-law. Pk G(n, p) Example: 6/17 (∀x ∃y (x ∼ y)) ∧ (∀x ∃y ¬(x ∼ y)) ∀x ∃y ∃z ((x ∼ y) ∧ (¬(x ∼ z))) Maksim Zhukovskii k=2 k=3 Critical points in zero-one laws for G(n, p)
  • 21. Zero-one k-laws Zhukovskii; 2010 (zero-one Let p=n If 7/17 −α k -law) , k ∈ N, k ≥ 3. 0α 1 k−2 then p ∈ Pk . Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 22. Zero-one k-laws Zhukovskii; 2010 (zero-one Let p=n If −α k -law) , k ∈ N, k ≥ 3. 0α 1 k−2 then p ∈ Pk . Zhukovskii; 2012+ (extension of zero-one Let p=n If 7/17 −α , k ∈ N, k ≥ 4, Q = α=1− 1 , 2k−1 +β {a, b a, b ∈ N, a ≤ 2k−1 } β ∈ (0, ∞) Q Maksim Zhukovskii k -law) then p ∈ Pk . Critical points in zero-one laws for G(n, p)
  • 23. Zero-one k-laws Zhukovskii; 2010 (zero-one Let p=n If −α k -law) , k ∈ N, k ≥ 3. 0α 1 k−2 then p ∈ Pk . Zhukovskii; 2012+ (extension of zero-one Let p=n If −α , k ∈ N, k ≥ 4, Q = α=1− 1 , 2k−1 +β 1− 1− ... 1 ,1 2k 1− 1  1 − k−1 2k−1 − 2 3 2 then p ∈ Pk . 1 1 ,1 − k 2k − 1 2 ,1 − Maksim Zhukovskii k -law) a, b ∈ N, a ≤ 2k−1 } β ∈ (0, ∞) Q 1 1 , 1 − k−1 2k−1 + 2k−2 2 + 2k−2 + 1  2k−1 + 7/17 {a, b 1− ... 1 2k−1 + 2k−1 −1 2 ,1 − 1 2k−1 + 2k−2  1 2k−1 + 2k−1 3   . . .? . . . 0, 1 k−2 Critical points in zero-one laws for . G(n, p)
  • 24. Zero-one k-laws Zhukovskii; 2013++ (no Let p=n −α k -law) , k ∈ N. If k ≥ 3, α = If 1 k−2 k ≥ 4, then ˜ Q=  k−1  2  k−1 − 2 · 1, . . . , 1;   2 −2·1−1·2 ,..., 1; 2 2  2k−1 −2·1−3·2−1·3 , . . . ;   5  ...; α=1− 8/17 p ∈ Pk . / 1 , 2k−1 +β ˜ β∈Q 2 k−1 −2·1−2·2 1 ,..., 3; 3 ...; ...; then k−1 −2·1−3·2 ,..., 1; 4 4 2k−1 −2·1−3·2−4·3 ,...; 8 2 ...          p ∈ Pk . / Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 25. Critical points 1−α: 0→1 9/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 26. Critical points 1−α: 0→1 0 9/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 27. Critical points 1−α: 0→1 0 9/17 1 2k Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 28. Critical points 1−α: 0→1 0 9/17 1 2k 1 2k −1 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 29. Critical points 1−α: 0→1 0 9/17 1 2k 1 2k −1 1 2k −2 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 30. Critical points 1−α: 0→1 0 9/17 1 2k 1 2k −1 1 2k −2 1 2k −3 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 31. Critical points 1−α: 0→1 0 9/17 1 2k 1 2k −1 1 2k −2 1 2k −3 ... Maksim Zhukovskii 1 2k −2k−2 Critical points in zero-one laws for G(n, p)
  • 32. Critical points 1−α: 0→1 0 9/17 1 2k 1 2k −1 1 2k −2 1 2k −3 ... Maksim Zhukovskii 1 2k −2k−2 ... Critical points in zero-one laws for G(n, p)
  • 33. Critical points 1−α: 0→1 0 1 2k 1 2k −1 Large gap: 9/17 1 2k −2 1 2k −3 ... 1 2k −2k−2 ... ? [1/2k−1 , 1 − 1/(k − 2)) Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 34. Critical points 1−α: 0→1 0 1 2k 1 2k −1 Large gap: 9/17 1 2k −2 1 2k −3 ... 1 2k −2k−2 ... ? 1− 1 k−2 [1/2k−1 , 1 − 1/(k − 2)) Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 35. Critical points 1−α: 0→1 0 Large gap: 9/17 1 2k −2 1 2k −3 ... 1 2k −2k−2 ... ? 1− 1 k−2 [1/2k−1 , 1 − 1/(k − 2)) Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 37. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 38. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 39. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 40. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 41. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 42. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 43. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 44. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 45. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 46. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 47. Ehrenfeucht game EHR(G, H, k) two graphs k number of rounds Spoiler Duplicator two players G, H 11/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 48. Ehrenfeucht theorem Theorem [A. Ehrenfeucht, 1960] Let G, H be two graphs. For any rst-order property L expressed by formula with quantier depth bounded by a number k G ∈ L ⇔ H ∈ L if and only if Duplicator has a winning strategy in the game EHR(G, H, k). Example: ∃x1 ∃x2 ∃x3 ((x1 ∼ x2) ∧ (x2 ∼ x3) ∧ (x1 ∼ x3)). 12/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 49. Ehrenfeucht theorem Theorem [A. Ehrenfeucht, 1960] Let G, H be two graphs. For any rst-order property L expressed by formula with quantier depth bounded by a number k G ∈ L ⇔ H ∈ L if and only if Duplicator has a winning strategy in the game EHR(G, H, k). Example: ∃x1 ∃x2 ∃x3 ((x1 ∼ x2) ∧ (x2 ∼ x3) ∧ (x1 ∼ x3)). 12/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 50. Ehrenfeucht theorem Theorem [A. Ehrenfeucht, 1960] Let G, H be two graphs. For any rst-order property L expressed by formula with quantier depth bounded by a number k G ∈ L ⇔ H ∈ L if and only if Duplicator has a winning strategy in the game EHR(G, H, k). Example: ∃x1 ∃x2 ∃x3 ((x1 ∼ x2) ∧ (x2 ∼ x3) ∧ (x1 ∼ x3)). 12/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 51. Proofs of k-laws Corollary Zero-one law holds if and only if for any k ∈ N almost surely Duplicator has a winning strategy in the Ehrenfeucht game on k rounds. Random graph G(n, p) obeys zero-one k-law if and only if almost surely Duplicator has a winning strategy in the Ehrenfeucht game on k rounds. 13/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 52. Case k = 4, α = 13/14 14/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 53. Case k = 4, α = 13/14 FISH GRAPH , , e = 14 v = 13 ρ = 14/13 14/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 54. Case k = 4, α = 13/14 FISH GRAPH , , G(n, n−13/14 ) contains a copy of FISH GRAPH with positive asymptotical probability; G(n, n−13/14 ) does not contain a copy of any graph with at most 13 vertices and maximal density at least 14/13 with positive asymptotical probability. e = 14 v = 13 ρ = 14/13 14/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 55. Case k = 4, α = 13/14 FISH GRAPH , , G(n, n−13/14 ) contains a copy of FISH GRAPH with positive asymptotical probability; G(n, n−13/14 ) does not contain a copy of any graph with at most 13 vertices and maximal density at least 14/13 with positive asymptotical probability. EHR(G, H, 4): e = 14 v = 13 ρ = 14/13 14/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 56. Case k = 4, α = 13/14 FISH GRAPH , , G(n, n−13/14 ) contains a copy of FISH GRAPH with positive asymptotical probability; G(n, n−13/14 ) does not contain a copy of any graph with at most 13 vertices and maximal density at least 14/13 with positive asymptotical probability. EHR(G, H, 4): G contains FISH GRAPH; e = 14 v = 13 ρ = 14/13 14/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 57. Case k = 4, α = 13/14 FISH GRAPH , , G(n, n−13/14 ) contains a copy of FISH GRAPH with positive asymptotical probability; G(n, n−13/14 ) does not contain a copy of any graph with at most 13 vertices and maximal density at least 14/13 with positive asymptotical probability. EHR(G, H, 4): G contains FISH GRAPH; H does not contain a copy of any graph with at most 13 vertices and maximal density at least 14/13. e = 14 v = 13 ρ = 14/13 14/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 58. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 59. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 60. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 61. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 62. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 63. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 64. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 65. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 66. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 67. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 68. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 69. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 70. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 71. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 72. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 73. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 74. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 75. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 76. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 77. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 78. Winning strategy of Spoiler 15/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 79. Open questions What happens when α ∈ 16/17 1 k−2 , 1 Maksim Zhukovskii − 1 2k−1 ? Critical points in zero-one laws for G(n, p)
  • 80. Open questions What happens when α ∈ 1 k−2 , 1 − 1 2k−1 ? Spencer and Shelah, 1988: There exists a rst-order property and an innite set S of rational numbers from (0, 1) such that for any α ∈ S random graph G(n, n−α ) follows the property with probability which doesn't tend to 0 or to 1. 16/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 81. Open questions What happens when α ∈ 1 k−2 , 1 − 1 2k−1 ? Spencer and Shelah, 1988: There exists a rst-order property and an innite set S of rational numbers from (0, 1) such that for any α ∈ S random graph G(n, n−α ) follows the property with probability which doesn't tend to 0 or to 1. For any xed k and any ε 0 in 1 − 2 1 + ε, 1 there is only nite number of critical points. Does this property holds for 1 − 2 1 , 1 ? Are there any other such subintervals in 1 1 ? k−2 , 1 − 2 k−1 k−1 k−1 16/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)
  • 82. Thank you! Thank you very much for your attention! 17/17 Maksim Zhukovskii Critical points in zero-one laws for G(n, p)