let G be Group; :: thesis: for H, N being normal Subgroup of G st N is Subgroup of H holds
ex M being strict normal Subgroup of G st the carrier of M = N ` H

let H, N be normal Subgroup of G; :: thesis: ( N is Subgroup of H implies ex M being strict normal Subgroup of G st the carrier of M = N ` H )
assume A1: N is Subgroup of H ; :: thesis: ex M being strict normal Subgroup of G st the carrier of M = N ` H
then consider M being strict Subgroup of G such that
A2: the carrier of M = N ` H by Th72;
for x being Element of G holds x * M c= M * x
proof
let x be Element of G; :: thesis: x * M c= M * x
let y be object ; :: according to TARSKI:def 3 :: thesis: ( not y in x * M or y in M * x )
assume A3: y in x * M ; :: thesis: y in M * x
then reconsider y = y as Element of G ;
consider z being Element of G such that
A4: ( y = x * z & z in M ) by ;
z in the carrier of M by ;
then A5: z * N c= carr H by ;
z in z * N by GROUP_2:108;
then z in H by ;
then (x * z) * (x ") in H by Th4;
then A6: ((x * z) * (x ")) * H = carr H by GROUP_2:113;
((x * z) * (x ")) * N c= ((x * z) * (x ")) * H by ;
then (x * z) * (x ") in N ` H by A6;
then A7: (x * z) * (x ") in M by ;
((x * z) * (x ")) * x = y by ;
hence y in M * x by ; :: thesis: verum
end;
then M is normal Subgroup of G by GROUP_3:118;
hence ex M being strict normal Subgroup of G st the carrier of M = N ` H by A2; :: thesis: verum