Changes http://wiki.axiom-developer.org/343BugInFreeAbelianGroup/diff
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The order in FreeAbelianGroup is broken and makes the domain unusable
(e.g., comparison of Set FreeAbelianGroup S does not work properly)
For example here is a cycle:

----------------------------------------
Z2:=FreeAbelianGroup Symbol         

a:= a::FreeAbelianGroup Symbol         
b:= b::FreeAbelianGroup Symbol
z:= 0::FreeAbelianGroup Symbol

a < -b 
-b < z
z < a
----------------------------------------

thus a < -b < z < a

proposed patch in the last few lines of free.spad:

545,546c545,546
<         ta.gen < tb.gen => true
<         ta.gen > tb.gen => false
---
>         ta.gen < tb.gen => tb.exp > 0
>         ta.gen > tb.gen => ta.exp < 0


apparently revlex order is intended but is not achieved in the current 
implementation,
as the sign of the trailing exponent is not taken into account.

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