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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_le_compat : forall r1 r2 r3 r4, r1 <= r2 -> r3 <= r4 -> r1 + r3 <= r2 + r4.