--- /dev/null
+
+include "logic/equality.ma".
+(* Inclusion of: ROB002-1.p *)
+(* -------------------------------------------------------------------------- *)
+(* File : ROB002-1 : TPTP v3.1.1. Released v1.0.0. *)
+(* Domain : Robbins Algebra *)
+(* Problem : --X = X => Boolean *)
+(* Version : [Win90] (equality) axioms. *)
+(* English : If --X = X then the algebra is Boolean. *)
+(* Refs : [HMT71] Henkin et al. (1971), Cylindrical Algebras *)
+(* : [Win90] Winker (1990), Robbins Algebra: Conditions that make a *)
+(* Source : [Win90] *)
+(* Names : Lemma 2.1 [Win90] *)
+(* Status : Unsatisfiable *)
+(* Rating : 0.00 v2.2.1, 0.11 v2.2.0, 0.14 v2.1.0, 0.13 v2.0.0 *)
+(* Syntax : Number of clauses : 5 ( 0 non-Horn; 5 unit; 1 RR) *)
+(* Number of atoms : 5 ( 5 equality) *)
+(* Maximal clause size : 1 ( 1 average) *)
+(* Number of predicates : 1 ( 0 propositional; 2-2 arity) *)
+(* Number of functors : 4 ( 2 constant; 0-2 arity) *)
+(* Number of variables : 8 ( 0 singleton) *)
+(* Maximal term depth : 6 ( 3 average) *)
+(* Comments : Commutativity, associativity, and Huntington's axiom *)
+(* axiomatize Boolean algebra. *)
+(* -------------------------------------------------------------------------- *)
+(* ----Include axioms for Robbins algebra *)
+(* Inclusion of: Axioms/ROB001-0.ax *)
+(* -------------------------------------------------------------------------- *)
+(* File : ROB001-0 : TPTP v3.1.1. Released v1.0.0. *)
+(* Domain : Robbins algebra *)
+(* Axioms : Robbins algebra axioms *)
+(* Version : [Win90] (equality) axioms. *)
+(* English : *)
+(* Refs : [HMT71] Henkin et al. (1971), Cylindrical Algebras *)
+(* : [Win90] Winker (1990), Robbins Algebra: Conditions that make a *)
+(* Source : [OTTER] *)
+(* Names : Lemma 2.2 [Win90] *)
+(* Status : *)
+(* Syntax : Number of clauses : 3 ( 0 non-Horn; 3 unit; 0 RR) *)
+(* Number of literals : 3 ( 3 equality) *)
+(* Maximal clause size : 1 ( 1 average) *)
+(* Number of predicates : 1 ( 0 propositional; 2-2 arity) *)
+(* Number of functors : 2 ( 0 constant; 1-2 arity) *)
+(* Number of variables : 7 ( 0 singleton) *)
+(* Maximal term depth : 6 ( 3 average) *)
+(* Comments : *)
+(* -------------------------------------------------------------------------- *)
+(* -------------------------------------------------------------------------- *)
+(* -------------------------------------------------------------------------- *)
+theorem prove_huntingtons_axiom:
+ \forall Univ:Set.
+\forall a:Univ.
+\forall add:\forall _:Univ.\forall _:Univ.Univ.
+\forall b:Univ.
+\forall negate:\forall _:Univ.Univ.
+\forall H0:\forall X:Univ.eq Univ (negate (negate X)) X.
+\forall H1:\forall X:Univ.\forall Y:Univ.eq Univ (negate (add (negate (add X Y)) (negate (add X (negate Y))))) X.
+\forall H2:\forall X:Univ.\forall Y:Univ.\forall Z:Univ.eq Univ (add (add X Y) Z) (add X (add Y Z)).
+\forall H3:\forall X:Univ.\forall Y:Univ.eq Univ (add X Y) (add Y X).eq Univ (add (negate (add a (negate b))) (negate (add (negate a) (negate b)))) b
+.
+intros.
+autobatch paramodulation timeout=100;
+try assumption.
+print proofterm.
+qed.
+(* -------------------------------------------------------------------------- *)