fact: Definition Stern_prev_fct x (y := (- x)^-1) := y - 1 - (floorq y)%:Q * 2%:Q.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype order bigop ssralg) mathcomp(div ssrnum ssrint rat prime path binomial) mathcomp(tuple finset) gaia(fibm)