% Mizar problem: t69_enumset1,enumset1,825,5 
fof(t69_enumset1, conjecture,  (! [A] :  (! [B] :  (! [C] :  (! [D] : k2_enumset1(A, B, C, D)=k2_enumset1(B, D, A, C)) ) ) ) ).
fof(dt_k2_enumset1, axiom, $true).
fof(l80_enumset1, axiom,  (! [A] :  (! [B] :  (! [C] :  (! [D] : k2_enumset1(A, B, C, D)=k2_enumset1(B, C, A, D)) ) ) ) ).
fof(t64_enumset1, axiom,  (! [A] :  (! [B] :  (! [C] :  (! [D] : k2_enumset1(A, B, C, D)=k2_enumset1(A, D, C, B)) ) ) ) ).
