fact: Definition subterms {s: sorts σ} (t: term σ s): (term σ)⋆ (arity (princop t)) := pr12 (term_decompose t).
imports: UniMath.MoreFoundations.Notations UniMath.MoreFoundations.PartA UniMath.Combinatorics.Maybe UniMath.Algebra.Universal.SortedTypes UniMath.Algebra.Universal.Signatures