@public
def vfree_group(symbols):
 _free_group = FreeGroup(symbols)
 pollute([sym.name for sym in _free_group.symbols], _free_group.generators)
 return _free_group

@ public def vfree_group ( symbols ) : _free_group = FreeGroup ( symbols ) pollute ( [ sym . name for sym in _free_group . symbols ] , _free_group . generators ) return _free_group
construct a free group and inject f_0 .