This document discusses three different healthcare payment systems in the United States: Medicare, Medigap, and Medicaid. It defines Medicare as a national health insurance program for the elderly and disabled, divided into parts A, B, C, and D. Medigap supplements Medicare by covering deductibles and coinsurance. Medicaid is a state-run program that provides coverage to low-income individuals if they meet eligibility requirements. The document compares the key differences between these payment systems and concludes with the author's new understanding of how they relate to each other.