(* Definition of the square root: R+->R *)
Definition Rsqrt (y:nonnegreal) : R :=
let (a,_) := Rsqrt_exists (nonneg y) (cond_nonneg y) in a.

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Lemma Rsqrt_Rsqrt : forall x:nonnegreal, Rsqrt x * Rsqrt x = x.