Applying Gödel's Dialectica Interpretation to Obtain a Constructive Proof of Higman's Lemma
Thomas Powell · Electronic Proceedings in Theoretical Computer Science · 2012
We use G\"odel'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.