fact: Definition eq' (x y : term') := ∀ x`[↑] ∈' $0 <~> y`[↑] ∈' $0.
imports: Undecidability.FOL.Util.Syntax Undecidability.FOL.Util.sig_bin Undecidability.FOL.Util.FullTarski Undecidability.FOL.Util.FullDeduction List