The constraints on the lowest order terms are as follows.

The higher order terms can be neglected in the limit .

By symmetry the odd order terms in the expansion are zero.

Accuracy can be increased indefinitely by considering higher order terms.

This expression is the leading order term of a Volterra-expansion.

Higher order terms in the series produce novel identities.

For small amplitudes, the higher order terms have little effect.

These can be called the next-to-leading order terms or corrections.

The cubic and higher order terms are assumed to be negligible.

The newer models generally provided higher order terms than their precursors.