include "basics/list.ma".
include "lambda-delta/xoa_defs.ma".
include "lambda-delta/xoa_notation.ma".
-include "lambda-delta/notation.ma".
(* ARITHMETICAL PROPERTIES **************************************************)
lemma minus_plus_comm: ∀a,b,c. a - b - c = a - (c + b).
// qed.
+lemma arith8: ∀a,b. a < a + b + 1.
+// qed.
+
+lemma arith9: ∀a,b,c. c < a + (b + c + 1) + 1.
+// qed.
+
lemma minus_le: ∀m,n. m - n ≤ m.
/2/ qed.