Equality is decidable on nat
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Lemma
not_eq_sym : (A:Set)(p,q:A)(~p=q) -> ~(q=p).
Proof
sym_not_eq.
Hints
Immediate
not_eq_sym : arith.
Require
Arith.
Require
Peano_dec.
Require
Compare_dec.
Definition
le_or_le_S := le_le_S_dec.
Definition
compare := gt_eq_gt_dec.
Lemma
le_dec : (n,m:nat) {le n m} + {le m n}.
Proof
le_ge_dec.
Definition
lt_or_eq := [n,m:nat]{(gt m n)}+{n=m}.
Lemma
le_decide : (n,m:nat)(le n m)->(lt_or_eq n m).
Proof
le_lt_eq_dec.
Lemma
le_le_S_eq : (p,q:nat)(le p q)->((le (S p) q)\/(p=q)).
Proof
le_lt_or_eq.
Lemma
discrete_nat : (m, n: nat) (lt m n) ->
(S m) = n \/ (EX r: nat | n = (S (S (plus m r)))).
Proof
.
Intros m n H.
LApply (lt_le_S m n); Auto with arith.
Intro H'; LApply (le_lt_or_eq (S m) n); Auto with arith.
NewInduction 1; Auto with arith.
Right; Exists (minus n (S (S m))); Simpl.
Rewrite (plus_sym m (minus n (S (S m)))).
Rewrite (plus_n_Sm (minus n (S (S m))) m).
Rewrite (plus_n_Sm (minus n (S (S m))) (S m)).
Rewrite (plus_sym (minus n (S (S m))) (S (S m))); Auto with arith.
Qed
.
Require
Export
Wf_nat.
Require
Export
Min.