fact: Definition s_pos (i j : nat) : ty := if Nat.eqb i j then mk_ty [isl] else (if Nat.eqb i (S j) then mk_ty [isr] else mk_ty [bullet]).
imports: Undecidability.IntersectionTypes.CD Undecidability.IntersectionTypes.Util.CD_facts Undecidability.StringRewriting.SSTS Undecidability.LambdaCalculus.Util.term_facts Relations List PeanoNat Lia ssreflect ssrfun