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(*         *   The Coq Proof Assistant / The Coq Development Team       *)
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Local Open Scope R_scope.
(* Proving a few formulas in the style of John Machin to compute Pi *)
Definition atan_sub u v := (u - v)/(1 + u * v).

Lemma Machin_2_3_7 : PI/4 = 2 * atan(/3) + (atan (/7)).