Calculating Maximal Order Types for Finite Rooted Unstructured Labeled Trees

Abstract

Diana Schmidt, in her Habilitationsschrift in 1979, completely classified the maximal order types of the natural tree embeddability relations for finite rooted structured labeled trees. Her results since have found interesting applications in proof theory and reverse mathematics. The question concerning the maximal order types of unstructured trees has been left open for years, and a conclusive answer will be given in this article. Moreover, we provide an answer to a question of Harvey Friedman regarding Γ 0 and binary two-labeled unstructured trees.