Normal, usual, typicalDefinite, strict, proper, all, someAny:数学表达中避免使用,all/someIntractable, infeasibleAn algorithm or problem is “intractable” only if it is NP-hard, that is, the asymptotic cost (or computational complexity) is believed to be worse than polynomial.in the context of an optimization problem, “infeasible” might mean that the problem has no (feasible) solution