DExt(M,N), DExt(M,N,w)
The procedure calls Drestriction, which uses w if specified.
The algorithm used appears in the paper 'Polynomial and rational solutions of holonomic systems' by OakuTakayamaTsai (2000). The method is to combine isomorphisms of Bjork and Kashiwara with the restriction algorithm.




The object DExt is a method function with options.