qed.
(*** minus_minus_comm *)
-lemma nminus_minus_comm (o) (m) (n): o - m - n = o - n - m.
+lemma nminus_comm (o) (m) (n): o - m - n = o - n - m.
#o #m #n @(nat_ind_succ … n) -n //
-qed-.
+qed.
+
+(*** minus_minus_comm3 *)
+lemma nminus_comm_231 (n) (m1) (m2) (m3):
+ n-m1-m2-m3 = n-m2-m3-m1.
+// qed.