I have been searching for a lemma in ssreflect
that represents sum linearity, so that I could transform
sum(a) + sum(b) = sum(c)
into
sum(a+b) =sum(c)
and then derive into
a+b = c.
Which could be suitable in this case?
The goal:
\big[Rplus/0]_(i <- fin_img (A:=U) (B:=R_eqType) X) (. . .) +
\big[Rplus/0]_(i <- fin_img (A:=U) (B:=R_eqType) X) (. . .) =
\sum_(u in U) X u * `p_ X u
I think you are looking for the big_split
lemma. But it is hard to know without knowing what goal you're trying to prove in more detail...