necessary condition and sufficient condition

So it's a sufficient condition for an argument being valid that there is no possible situation where the premises are true and the conclusion false. And that's a necessary condition too.

所以这对于论点有效性是充分条件，没有可能前提为真，结论为假，这是必要条件。

Moreover, a judgement condition for live and bound WAC net system is given, and the sufficient and necessary condition for WAC net liveness monotonicity is shown.

同时，提出了活的有界的WAC网系统的判定条件，进而给出了WAC网活性满足单调性的充分必要条件。

Besides, this paper gives a sufficient and necessary condition of the existence of normal process under the strictly nonnegative definiteness condition.

此外本文还给出了严格非负定条件下实正态过程存在的一个充要条件。