for x, y being Element of BOOLEAN holds
( inv1 . <*(xor2 . <*x,y*>)*> = xor2a . <*x,y*> & inv1 . <*(xor2 . <*x,y*>)*> = xor2c . <*x,y*> & xor2 . <*(inv1 . <*x*>),(inv1 . <*y*>)*> = xor2 . <*x,y*> )