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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 Rplus_neg_npos : forall r1 r2, r1 < 0 -> r2 <= 0 -> r1 + r2 < 0.