Update src/sage/rings/polynomial/multi_polynomial_sequence.py

Co-authored-by: Vincent Neiger <[email protected]>

Author: MercedesHaiech

src/sage/rings/polynomial/multi_polynomial_sequence.py

@@ -1102,7 +1102,7 @@ def macaulay_matrix(self, degree,
             else:
                 R_monomials_useful = []
                 for i in range(degree,target_degree-self.minimal_degree()+1):
-                    R_monomials_useful+=R_monomials_of_degree[i]
+                    R_monomials_useful += R_monomials_of_degree[i]
                 R_monomials_useful.sort()
                 for mon in R_monomials_useful:
                     row_indices += [(mon, i) for i in range(m) if self[i].degree() + mon.degree()==target_degree]