let Y be non empty set ; :: thesis:
let a, b, c be Element of Funcs (Y,BOOLEAN); :: thesis:
consider k3 being Function such that
A1: (a '&' b) 'imp' c = k3 and
A2: dom k3 = Y and
rng k3 c= BOOLEAN by FUNCT_2:def 2;
consider k4 being Function such that
A3: a 'imp' (('not' b) 'or' c) = k4 and
A4: dom k4 = Y and
rng k4 c= BOOLEAN by FUNCT_2:def 2;
for x being Element of Y holds ((a '&' b) 'imp' c) . x = (a 'imp' (('not' b) 'or' c)) . x

let x be Element of Y; :: thesis:
(a 'imp' (('not' b) 'or' c)) . x = (a 'imp' (b 'imp' c)) . x by BVFUNC_4:8;
hence ((a '&' b) 'imp' c) . x = (a 'imp' (('not' b) 'or' c)) . x by Th7; :: thesis:

end;