[GAP Forum] finding automorphisms of finitely presented groups

[Robert Heffernan]

Thank you for your help Alexander.
I do have a followup question, if anybody can help.
I have created a finitely presented group G
F:=FreeGroup("a","b","c","d");;a:=F.1;;b:=F.2;;c:=F.3;;d:=F.4;;rels:= <some words in terms of a,b,c and d>G:=F/rels;a:=G.1;;b:=G.2;;c:=G.3;;d:=G.4;;
I have then created a new set of words/relations, rels2 say, in termsof a,b,c and d (by calculating with things in G).
Now I want to create a new finitely presented group in a manner such as this:H:=F/rels2;
However, I can't do this directly as a,b,c and d are now elements of G, not F.
I can't find a simple way to relate a,b,c and d back to the generatorsof the free group F, even though I'm sure such a thing must exist.
Any help would be wonderful.
thank you,Bob