Internal implementation for RingDistrMPolyClean
The primary purpose for object of class DistrMPolyClean is to represent
values in a RingDistrMPolyClean; consequently all operations on a
DistrMPolyClean which could allocate or deallocate memory must take
arguments indicating which memory manager(s) to use.
An object of type DistrMPolyClean is essentially an ordered (singly) linked
list of summands, and each summand is a pair made up of a coefficient
(held as a RingElem) and a power product (held as a PPMonoidElem). In a
valid DistrMPoly all the coefficients are non-zero, the power products
are all distinct and the summands are ordered decreasingly according to
the ordering on the PPs (as determined by the PPO inside the owning
PPMonoid).