def _dummy(name, token, expr, **kwargs):
 d = _dummy_(name, token, **kwargs)
 if (d in expr.free_symbols):
  return Dummy(name, **kwargs)
 return d

def _dummy ( name , token , expr , ** kwargs ) : d = _dummy_ ( name , token , ** kwargs ) if ( d in expr . free_symbols ) : return Dummy ( name , ** kwargs ) return d
return a dummy .