-- keyword for an optional argument used with resolution
which indicates how long a resolution to make.
For polynomial rings over a field or over the integers, the length is taken to be the dimension of the ring, so the complete resolution will be obtained. For quotient rings of such rings, the same number is used, so the complete resolution may not be obtained.
In the current version, asking for a second and longer resolution of the same module involves recomputing the resolution from scratch. Eventually the previous work will be used and the recomputation will go quicker.
The resolution returned may actually be one step longer than requested. The extra differential is not guaranteed to be minimal.