该句中的never to be found如何解释,是什么语法现象?

问题描述:

该句中的never to be found如何解释,是什么语法现象?
Lily's mobile phone was left in a taxi accidentally,never to be found again.

不定式作结果状语,可以改成第二个句子.Lily's mobile phone was left in a taxi accidentally and it has never been found again.又如:He left home,never to be heard of again.他离开了,再也没有人听过他的消息....