20260219

• bugfix for low values of -f
• new option -fr

bugfix for low values of -f

Given -f<a>, with $a < p < k$, we can fail to allocate powers of $p$ at positions such that only one power of $p$ is needed when searching for $D(n, k)$.

new option -fr

When this option is specified, -px restrictions apply also to fixed primes. This should be considered an experimental option: it applies only restrictions on maximum power (not on minimum power), and does not affect -W handling at all.