manhattan 例句 求解

shannii

这个句子出现在manhattan语法的第三章 主谓一致 flip 倒装句正序里面。句子能看懂就没仔细分析过，今天看突然转不过来了。Pong is a classic game from which HAVE descended many current computer pastimes.
分析如下，

主句是 Pong is a classic game.

后面是定语 from which HAVE descended many current computer pastimes

是一个倒装， flip之后是 Current computer pastimes may have descended from which

但是经常见介宾短语作定语的情况 都是跟在逗号之后。

eg There is a house, in front of which stands a boy.

所以这种情况，逗号不是必须？求指教。