asynchable commit

A σ-quasiconvex subgroup of an asynchronously combable group is also asynchronously combable,and furthermore,a σ-quasiconvex subgroup of an asynchronously combable group equipped with a departure function is also asynchronously combable equipped with a departure function.

证明了异步可梳群的σ-拟凸子群仍是异步可梳群,并且如果异步可梳群具有分离函数,则其σ-拟凸子群也具有分离函数。