If we want to change this (required for incomplete decompositions) then we have to extend the structured format
and add a Lambda for the denominator to the ``(r, nf, ex)`` triple giving a ``(r, nd, df, ex)`` quadruple. In case of
full decomposition, ``df`` would always be ``Lambda([a], (x-a))`` or similar. It seems that providing this information
also in the case it's not necessary is wrong. Any comments on this?