limit variable separation to cases involving at most 7 variables
limit variable separation to cases involving at most 7 variables

There may be a way to make the separation more efficient, so that also
more variables can be processed.

edechter/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,edechter/swipl-devel