in other words, we know that the result of applying the bridge to the document resulting from c will be precisely the document state before applying e, thus we can cleanly compose e with the bridge.
换句话说,我们知道对操作c作用之后的文档应用该桥梁所得的结果恰好就是应用e之前的文档状态,因此,我们可以简洁清楚的组合e和桥。