let C be initialized ConstructorSignature; :: thesis: for t1, t2, t being expression of C st t is_a_unification_of t1,t2 holds
t is_a_unification_of t2,t1
let t1, t2, t be expression of C; :: thesis: ( t is_a_unification_of t1,t2 implies t is_a_unification_of t2,t1 )
given f being valuation of C such that A1: ( f unifies t1,t2 & t = t1 at f ) ; :: according to ABCMIZ_A:def 27 :: thesis: t is_a_unification_of t2,t1
take f ; :: according to ABCMIZ_A:def 27 :: thesis: ( f unifies t2,t1 & t = t2 at f )
thus ( f unifies t2,t1 & t = t2 at f ) by A1; :: thesis: verum