Dear all,

I need to do something which I thought would be quite simple. I have free 
groups
F, G with generators x1,x2,x3,x4 and x,y respectively and I need to compute 
the image of an element under the homomorphism F-->G:x1->x, x2->y, x3->x, 
x4->y.

I could not find anything in the manual about morphisms between free 
groups. I tried subs, but that does not work since the parents of the 
elements of F and G are (of course) different.

The workaround I used is to work in the free group H with generators 
x1,x2,x3,x4,x,y and to use subs. However this is also inconvenient since I 
need the action of the braid group with 4 strands on F. It does not act on 
H because of the limitation "#strands=#generators".

So this means I have to use only part of the braid group with 6 strands.

In the end it all works but it is terribly hacky for some which seems to be 
a very clean thing to do.

I would be grateful for any suggestions.
Michel
 

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