let I be set ; :: thesis: for A being ManySortedSet of
for B, C being V2() ManySortedSet of
for F being ManySortedFunction of A,B
for G being ManySortedFunction of B,C
for X being ManySortedSubset of A holds (G ** F) || X = G ** (F || X)

let A be ManySortedSet of ; :: thesis: for B, C being V2() ManySortedSet of
for F being ManySortedFunction of A,B
for G being ManySortedFunction of B,C
for X being ManySortedSubset of A holds (G ** F) || X = G ** (F || X)

let B, C be V2() ManySortedSet of ; :: thesis: for F being ManySortedFunction of A,B
for G being ManySortedFunction of B,C
for X being ManySortedSubset of A holds (G ** F) || X = G ** (F || X)

let F be ManySortedFunction of A,B; :: thesis: for G being ManySortedFunction of B,C
for X being ManySortedSubset of A holds (G ** F) || X = G ** (F || X)

let G be ManySortedFunction of B,C; :: thesis: for X being ManySortedSubset of A holds (G ** F) || X = G ** (F || X)
let X be ManySortedSubset of A; :: thesis: (G ** F) || X = G ** (F || X)
now
let i be set ; :: thesis: ( i in I implies ((G ** F) || X) . i = (G ** (F || X)) . i )
assume A1: i in I ; :: thesis: ((G ** F) || X) . i = (G ** (F || X)) . i
then reconsider gf = (G ** F) . i as Function of (A . i),(C . i) by PBOOLE:def 18;
reconsider f = F . i as Function of (A . i),(B . i) by A1, PBOOLE:def 18;
reconsider g = G . i as Function of (B . i),(C . i) by A1, PBOOLE:def 18;
reconsider fx = (F || X) . i as Function of (X . i),(B . i) by A1, PBOOLE:def 18;
thus ((G ** F) || X) . i = gf | (X . i) by A1, MSAFREE:def 1
.= (g * f) | (X . i) by A1, MSUALG_3:2
.= g * (f | (X . i)) by RELAT_1:112
.= g * fx by A1, MSAFREE:def 1
.= (G ** (F || X)) . i by A1, MSUALG_3:2 ; :: thesis: verum
end;
hence (G ** F) || X = G ** (F || X) by PBOOLE:3; :: thesis: verum