A COMPUTABLE ANALYSIS OF VARIABLE WORDS THEOREMS

作者:Liu, Lu*; Monin, Benoit; Patey, Ludovic
来源:PROCEEDINGS OF THE AMERICAN MATHEMATICAL SOCIETY, 2019, 147(2): 823-834.
DOI:10.1090/proc/14269

摘要

The Carlson-Simpson lemma is a combinatorial statement occurring in the proof of the Dual Ramsey theorem. Formulated in terms of variable words, it informally asserts that given any finite coloring of the strings, there is an infinite sequence with infinitely many variables such that for every valuation, some specific set of initial segments is homogeneous. Friedman, Simpson, and Montalban asked about its reverse mathematical strength. We study the computability-theoretic properties and the reverse mathematics of this statement, and relate it to the finite union theorem. In particular, we prove the Ordered Variable word for binary strings in ACA(0).