let Y be non empty set ; :: thesis: for a being Function of Y,BOOLEAN holds (I_el Y) 'imp' a = a
let a be Function of Y,BOOLEAN; :: thesis: (I_el Y) 'imp' a = a
let x be Element of Y; :: according to FUNCT_2:def 8 :: thesis: K11(((I_el Y) 'imp' a),x) = K11(a,x)
((I_el Y) 'imp' a) . x = ('not' ((I_el Y) . x)) 'or' (a . x) by BVFUNC_1:def 8
.= FALSE 'or' (a . x) by BVFUNC_1:def 11 ;
hence K11(((I_el Y) 'imp' a),x) = K11(a,x) ; :: thesis: verum