deffunc H₂( Element of BOOLEAN , Element of BOOLEAN ) -> Element of BOOLEAN = ('not' $1) 'xor' $2;
thus for t1, t2 being Function of (2 -tuples_on BOOLEAN),BOOLEAN st ( for x, y being Element of BOOLEAN holds t1 . <*x,y*> = H₂(x,y) ) & ( for x, y being Element of BOOLEAN holds t2 . <*x,y*> = H₂(x,y) ) holds
t1 = t2 from FACIRC_1:sch 2(); :: thesis: verum