let Y be non empty set ; :: thesis: for G being Subset of (PARTITIONS Y)
for a, b being Element of Funcs Y,BOOLEAN
for PA being a_partition of Y holds a 'imp' b '<' a 'imp' (Ex b,PA,G)
let G be Subset of (PARTITIONS Y); :: thesis: for a, b being Element of Funcs Y,BOOLEAN
for PA being a_partition of Y holds a 'imp' b '<' a 'imp' (Ex b,PA,G)
let a, b be Element of Funcs Y,BOOLEAN ; :: thesis: for PA being a_partition of Y holds a 'imp' b '<' a 'imp' (Ex b,PA,G)
let PA be a_partition of Y; :: thesis: a 'imp' b '<' a 'imp' (Ex b,PA,G)
let z be Element of Y; :: according to BVFUNC_1:def 15 :: thesis: ( not (a 'imp' b) . z = TRUE or (a 'imp' (Ex b,PA,G)) . z = TRUE )
assume (a 'imp' b) . z = TRUE ; :: thesis: (a 'imp' (Ex b,PA,G)) . z = TRUE
then A1: ('not' (a . z)) 'or' (b . z) = TRUE by BVFUNC_1:def 11;
A2: ( 'not' (a . z) = TRUE or 'not' (a . z) = FALSE ) by XBOOLEAN:def 3;
A3: ( z in EqClass z,(CompF PA,G) & EqClass z,(CompF PA,G) in CompF PA,G ) by EQREL_1:def 8;

per cases ( 'not' (a . z) = TRUE or b . z = TRUE ) by A1, A2, BINARITH:7;

suppose 'not' (a . z) = TRUE ; :: thesis: (a 'imp' (Ex b,PA,G)) . z = TRUE

hence (a 'imp' (Ex b,PA,G)) . z = TRUE 'or' ((Ex b,PA,G) . z) by BVFUNC_1:def 11
.= TRUE by BINARITH:19 ;
:: thesis: verum

end;

suppose b . z = TRUE ; :: thesis: (a 'imp' (Ex b,PA,G)) . z = TRUE

then (B_SUP b,(CompF PA,G)) . z = TRUE by A3, BVFUNC_1:def 20;
then (Ex b,PA,G) . z = TRUE by BVFUNC_2:def 10;
hence (a 'imp' (Ex b,PA,G)) . z = ('not' (a . z)) 'or' TRUE by BVFUNC_1:def 11
.= TRUE by BINARITH:19 ;
:: thesis: verum

end;

end;