Find a list of list from a Matrix

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Suppose I have a matrix say

L=[[1,2],[3, 4]]
M=matrix(L)

then after a few operations M is transformed in N say

N = matrix([[10,12],[33,14]])

how can I obtain the list NN = [[10,12],[33,14]].

If know that N.coefficients() = N.list() = [10,12,33,14] but what I want is [[10,12],[33,14]].