let X be set ; :: thesis: for S being non empty Subset-Family of X
for N, G, F being sequence of S st G . 0 = N . 0 & ( for n being Nat holds G . (n + 1) = (N . (n + 1)) \/ (G . n) ) & F . 0 = N . 0 & ( for n being Nat holds F . (n + 1) = (N . (n + 1)) \ (G . n) ) holds
for n, m being Nat st n <= m holds
F . n c= G . m

let S be non empty Subset-Family of X; :: thesis: for N, G, F being sequence of S st G . 0 = N . 0 & ( for n being Nat holds G . (n + 1) = (N . (n + 1)) \/ (G . n) ) & F . 0 = N . 0 & ( for n being Nat holds F . (n + 1) = (N . (n + 1)) \ (G . n) ) holds
for n, m being Nat st n <= m holds
F . n c= G . m

let N, G, F be sequence of S; :: thesis: ( G . 0 = N . 0 & ( for n being Nat holds G . (n + 1) = (N . (n + 1)) \/ (G . n) ) & F . 0 = N . 0 & ( for n being Nat holds F . (n + 1) = (N . (n + 1)) \ (G . n) ) implies for n, m being Nat st n <= m holds
F . n c= G . m )

assume that
A1: G . 0 = N . 0 and
A2: for n being Nat holds G . (n + 1) = (N . (n + 1)) \/ (G . n) and
A3: F . 0 = N . 0 and
A4: for n being Nat holds F . (n + 1) = (N . (n + 1)) \ (G . n) ; :: thesis: for n, m being Nat st n <= m holds
F . n c= G . m

let n, m be Nat; :: thesis: ( n <= m implies F . n c= G . m )
A5: for n being Nat holds F . n c= G . n
proof
defpred S1[ Nat] means F . \$1 c= G . \$1;
A6: for n being Nat st S1[n] holds
S1[n + 1]
proof
let n be Nat; :: thesis: ( S1[n] implies S1[n + 1] )
assume F . n c= G . n ; :: thesis: S1[n + 1]
G . (n + 1) = (N . (n + 1)) \/ (G . n) by A2;
then A7: N . (n + 1) c= G . (n + 1) by XBOOLE_1:7;
F . (n + 1) = (N . (n + 1)) \ (G . n) by A4;
hence S1[n + 1] by ; :: thesis: verum
end;
A8: S1[ 0 ] by A1, A3;
thus for n being Nat holds S1[n] from NAT_1:sch 2(A8, A6); :: thesis: verum
end;
A9: ( n < m implies F . n c= G . m )
proof
assume n < m ; :: thesis: F . n c= G . m
then A10: G . n c= G . m by A1, A2, Th6;
F . n c= G . n by A5;
hence F . n c= G . m by A10; :: thesis: verum
end;
assume n <= m ; :: thesis: F . n c= G . m
then ( n = m or n < m ) by XXREAL_0:1;
hence F . n c= G . m by A5, A9; :: thesis: verum