Function: format-subtract-regions

Remove from the regions in MINUEND the regions in SUBTRAHEND.
A region is a dotted pair (FROM . TO). Both parameters are lists of
regions. Each list must contain nonoverlapping, noncontiguous
regions, in descending order. The result is also nonoverlapping,
noncontiguous, and in descending order. The first element of MINUEND
can have a cdr of nil, indicating that the end of that region is not
yet known.