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If a division by 0 occurs, i.e.
and Sn(q)=0, then we try to prove (recursively) that q is
If it is true, then the original expression does not make
If we have proof that the denominator is not zero, this means
that we have found an n for which
and hence can continue computing the signature of the original
expression with this n.
If the division fails because
Sn(q) | n, when n is not
prime, then we can try with different values of n.
In some cases, when there are other restrictions on n,
it may not be possible to compute the division.
For example, if n is restricted to be a multiple of 2,
then the expression