theorem :: BCIALG_1:83

for X being non empty BCIStr_0 holds
( X is implicative BCI-algebra iff for x, y, z being Element of X holds
( ((x \ y) \ (x \ z)) \ (z \ y) = 0. X & x \ (0. X) = x & (x \ (x \ y)) \ (y \ x) = y \ (y \ x) ) )