(* Pythagorean.v *)
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(* Pythagorean triples *)
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Require Export Tactics.
(* A non nul predicate *)
Definition nnl_triple (a b c : Z) := ~(a = 0) /\ ~(b = 0) /\ ~(c = 0).
(* A positive predicate *)
Definition pos_triple (a b c : Z) := (a >= 0) /\ (b >= 0) /\ (c >= 0).
(* A Pythagorean predicate *)
Definition is_pytha (a b c : Z) := (pos_triple a b c) /\ a * a + b * b = c * c.
(* Unit circle and D_r *)
Definition in_ucirc (x y : R) := (x * x + y * y = 1)%R.
Definition D_r (r x y : R) := (y = r * (x + 1))%R.
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(* Set of Pythagorean triples *)
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(* step1 *)

Lemma pytha_ucirc2 : forall a b c : Z, (a >= 0) /\ (b >= 0) /\ (c > 0) ->
(in_ucirc (frac a c) (frac b c)) -> (is_pytha a b c).