Pawula theorem means that if truncating to the second term is not exact, that is, A 2 ≠ ≠ A , then truncating to any term is still not exact. Usually, this means that for any truncation A m , there exists a probability density function ρ ρ that can become negative during its evolution ∂ ∂ t ρ ρ ≈ ≈ A m ρ ρ (and thus fail to be a probability density function). However, this doesn't mean that Kramers-Moyal expansions truncated at other choices of m is useless. Though the solution must have negative values at least for sufficiently small times, the resulting approximation probability density may still be better than the m = 2 approximation.