Check the poly does have one and only one monomial with order n
poly (Poly) – conditional central moment of the state with keyfor = (‘e^{kt}’, ‘k^{-}’, ‘v0-E[v]’, ‘E[v]’, ‘sigma’, ‘lmbd’, ‘mu_v’)
keyfor
n (integer) – order of \(v0-E[v]\)
True or raise an error
bool