inaccessible element是什么意思

用法例句

However,whether or not there exists some modular-n S-invariant,which can be used to decide the non-reachability property of a marking?And if such modular-n S-invariant exists,how to find it?There is no answer to both of the .

Hohn F E提出用S-不变量判定Petri网不可达性的一个方法。