theorem :: BVFUNC_6:151

for Y being non empty set
for a, b, c, d being Function of Y,BOOLEAN holds ((a 'imp' b) '&' (b 'imp' c)) '&' (c 'imp' d) = ((a 'imp' ((b '&' c) '&' d)) '&' (b 'imp' (c '&' d))) '&' (c 'imp' d)