看到有一条理论说的是：当定语从句为there be 结构时，做主语的that可以省略，给出的例子是：I have told youallthere is to tell 假设此理论正确，可there is to tell不就是一个完整的主系表结构吗？that还如何做主语？
I have told you all there is to tell.
这句话，关系代词 that 是定语从句 there is to tell 的主语，可省略。to tell 是 that 的定语。完整的句子是如此的：
There is something to tell . ——that 指 something。
