Wtk(v). In particular, this basis is in a triangular form with regard to W¯tk(v), where W¯tk(v) is obtained from Wtk(v) by allowing its first
)−(vt) columns to be B1, . . . , B(vk)−(vt) in lexicographical ordering and its last
) columns to be the re-
maining elements of Pk(X) in lexicographical ordering as well.