diff'(Matrix,Matrix)  differentiate a matrix by a matrix, the dual notion
Synopsis

Function: diff'

 Usage:
h = diff'(m,n)

Inputs:

m, a map m : F < P between free modules of ranks f and p.

n, a map n : G < Q between free modules of ranks g and q.

Outputs:

h, a matrix with the shape h : F ** dual G < P ** dual Q, whose entry in the slot h_{g*i+j,q*k+l} is the result of differentiating n_{j,l}, by m_{i,k}