fix mistakes

Author: fchapoton

src/sage/algebras/cluster_algebra.py

@@ -1988,7 +1988,7 @@ def F_polynomial(self, g_vector):
                 msg += "you can compute it by mutating from the initial seed along the sequence "
                 msg += str(self._path_dict[g_vector])
                 raise KeyError(msg)
-            raise KeyError("the g-vector %s has not been found yet".format(g_vector))
+            raise KeyError("the g-vector {} has not been found yet".format(g_vector))
 
     def find_g_vector(self, g_vector, depth=infinity):
         r"""

src/sage/algebras/fusion_rings/f_matrix.py

@@ -1379,7 +1379,7 @@ def _map_triv_reduce(self, mapper, input_iter, worker_pool=None, chunksize=None,
         else:
             mapped = worker_pool.imap_unordered(executor, input_iter, chunksize=chunksize)
         # Reduce phase
-        results = {child_eqns for child_eqns in mapped
+        results = {eqn for child_eqns in mapped for eqn in child_eqns
                    if child_eqns is not None}
         return list(results)