SEPARATING PRINCIPLES BELOW RAMSEY'S THEOREM FOR PAIRS
Manuel Lerman, Reed Solomon, Henry Towsner · Journal of Mathematical Logic · 2013
In recent years, there has been a substantial amount of work in reverse mathematics concerning natural mathematical principles that are provable from RT, Ramsey's Theorem for Pairs. These principles tend to fall outside of the "big five" systems of reverse mathematics and a complicated picture of subsystems below RT has emerged. In this paper, we answer two open questions concerning these subsystems, specifically that ADS is not equivalent to CAC and that EM is not equivalent to RT.