2012/10/11 by Thomas Powell
Computer Science · #cs.LO #cs.DM
paper · pdf · doi:10.4204/eptcs.97.4
published as EPTCS 97, 2012, pp. 49-62 · In Proceedings CL&C 2012, arXiv:1210.2890
arxiv created 2012/10/11 · arxiv updated 2012/10/12
We use Gödel's Dialectica interpretation to analyse Nash-Williams' elegant but non-constructive "minimal bad sequence" proof of Higman's Lemma. The result is a concise constructive proof of the lemma (for arbitrary decidable well-quasi-orders) in which Nash-Williams' combinatorial idea is clearly present, along with an explicit program for finding an embedded pair in sequences of words.