+ optimize_pair GAS_assoc (GAS_second GAS_cancell) = Just $ GAS_first GAS_cancelr
+ optimize_pair GAS_unassoc (GAS_first GAS_cancell) = Just $ GAS_cancell
+
+
+ -- FIXME: valid only for central morphisms
+ --optimize_pair (GAS_second f) (GAS_first g) = Just $ GAS_comp (GAS_first g) (GAS_second f)
+ optimize_pair (GAS_first g) (GAS_second f) = Just $ GAS_comp (GAS_second f) (GAS_first g)