let A be set ; :: thesis: for a, b being Element of (NormForm A) holds (a "/\" b) "\/" b = b
let a, b be Element of (NormForm A); :: thesis: (a "/\" b) "\/" b = b
reconsider a9 = a, b9 = b as Element of Normal_forms_on A by Def12;
set G = NormForm A;
thus (a "/\" b) "\/" b = the L_join of (NormForm A) . (( the L_meet of (NormForm A) . (a9,b9)),b9)
.= b by Lm11 ; :: thesis: verum