for x, y being Element of BOOLEAN holds
( xor2 . <*x,y*> = x 'xor' y & xor2a . <*x,y*> = ('not' x) 'xor' y & xor2b . <*x,y*> = ('not' x) 'xor' ('not' y) ) by FACIRC_1:def 4, Def7, Def8;