theorem :: BVFUNC_6:78

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