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(** ** Square function                                   *)
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Definition Rsqr r : R := r * r.Notation "r ²" := (Rsqr r) (at level 1, format "r ²") : R_scope.

Lemma Rmult_le_pos : forall r1 r2, 0 <= r1 -> 0 <= r2 -> 0 <= r1 * r2.