fact: Definition fgadd g1 g2 := [malg k in msupp g1 `|` msupp g2 => g1@_k + g2@_k].
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap