inv_mcol
#define inv_mcol im_sub
#define inv_mcol(x) four_tables(x, t_use(i, m), vf1, rf1, 0)
#define inv_mcol(x) one_table(x, upr, t_use(i, m), vf1, rf1, 0)
#define inv_mcol(x) (g2 = gf_mulx(x), g4 = gf_mulx(g2), g9 = \