let Y be non empty set ; :: thesis: for G being Subset of (PARTITIONS Y)
for a, b being Function of Y,BOOLEAN
for PA being a_partition of Y holds (All (a,PA,G)) '&' (All (b,PA,G)) '<' a '&' b
let G be Subset of (PARTITIONS Y); :: thesis: for a, b being Function of Y,BOOLEAN
for PA being a_partition of Y holds (All (a,PA,G)) '&' (All (b,PA,G)) '<' a '&' b
let a, b be Function of Y,BOOLEAN; :: thesis: for PA being a_partition of Y holds (All (a,PA,G)) '&' (All (b,PA,G)) '<' a '&' b
let PA be a_partition of Y; :: thesis: (All (a,PA,G)) '&' (All (b,PA,G)) '<' a '&' b
let z be Element of Y; :: according to BVFUNC_1:def 12 :: thesis: ( not ((All (a,PA,G)) '&' (All (b,PA,G))) . z = TRUE or (a '&' b) . z = TRUE )
A1: ((All (a,PA,G)) '&' (All (b,PA,G))) . z = ((All (a,PA,G)) . z) '&' ((All (b,PA,G)) . z) by MARGREL1:def 20;
assume A2: ((All (a,PA,G)) '&' (All (b,PA,G))) . z = TRUE ; :: thesis: (a '&' b) . z = TRUE

A3: now :: thesis: for x being Element of Y st x in EqClass (z,(CompF (PA,G))) holds
a . x = TRUE

assume ex x being Element of Y st
( x in EqClass (z,(CompF (PA,G))) & not a . x = TRUE ) ; :: thesis: contradiction
then (B_INF (a,(CompF (PA,G)))) . z = FALSE by BVFUNC_1:def 16;
then (All (a,PA,G)) . z = FALSE by BVFUNC_2:def 9;
hence contradiction by A2, A1, MARGREL1:12; :: thesis: verum

end;

A4: z in EqClass (z,(CompF (PA,G))) by EQREL_1:def 6;

now :: thesis: for x being Element of Y st x in EqClass (z,(CompF (PA,G))) holds
b . x = TRUE

assume ex x being Element of Y st
( x in EqClass (z,(CompF (PA,G))) & not b . x = TRUE ) ; :: thesis: contradiction
then (B_INF (b,(CompF (PA,G)))) . z = FALSE by BVFUNC_1:def 16;
then (All (b,PA,G)) . z = FALSE by BVFUNC_2:def 9;
hence contradiction by A2, A1, MARGREL1:12; :: thesis: verum

end;

then A5: b . z = TRUE by A4;
thus (a '&' b) . z = (a . z) '&' (b . z) by MARGREL1:def 20
.= TRUE '&' TRUE by A4, A3, A5
.= TRUE ; :: thesis: verum