fact: Definition is_pair (x y t : term') := ∀ $0 ∈' t`[↑] <~> $0 ≡' x`[↑] ∨ $0 ≡' y`[↑].
imports: Undecidability.FOL.Util.Syntax Undecidability.FOL.Util.sig_bin Undecidability.FOL.Util.FullTarski Undecidability.FOL.Util.FullDeduction List