The setoid of vectors over a given setoid, defined using a function
0 .VectEquality : (a : Setoid) -> Rel (Vect n (U a))
index : (i : Fin n) -> a .VectEquality xs ys -> (a .equivalence) .relation (index i xs) (index i ys)
VectSetoid : Nat -> Setoid -> Setoid
VectMap : (a ~~> b) ~> (VectSetoid n a ~~> VectSetoid n b)