let Y be non empty set ; for a, b, c being Function of Y,BOOLEAN holds (a '&' b) 'imp' c = a 'imp' (('not' b) 'or' c)
let a, b, c be Function of Y,BOOLEAN; (a '&' b) 'imp' c = a 'imp' (('not' b) 'or' c)
let x be Element of Y; FUNCT_2:def 8 K11(((a '&' b) 'imp' c),x) = K11((a 'imp' (('not' b) 'or' c)),x)
(a 'imp' (('not' b) 'or' c)) . x = (a 'imp' (b 'imp' c)) . x
by BVFUNC_4:8;
hence
K11(((a '&' b) 'imp' c),x) = K11((a 'imp' (('not' b) 'or' c)),x)
by Th7; verum