(* Diophantus20.v *)
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(* Diophantus' 20th problem *)
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Require Export Descent.
Require Export Pythagorean.
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(* Some auxiliary lemmas *)
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(* Diophantus' problem *)
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Lemma diophantus20_refined : forall p q : Z,
p > 0 -> q > 0 -> p <= q -> rel_prime p q -> distinct_parity p q ->
~ is_sqr (p * (q * (q * q - p * p))).