Maxima Function
submatrix (i_1, ..., i_m, M, j_1, ..., j_n)
submatrix(i_1,...,i_m,M)
submatrix(M,j_1,...,j_n)
Returns a new matrix composed of the matrix M with rows i_1, ..., i_m deleted, and columns j_1, ..., j_n deleted.