There are not two in the room of a sibilant (śar), when a vowel follows.,
The word न is to be read into the sutra. This debars the application of rule 46 ante. Thus कर्षति, वर्षति, आकर्षः, अक्षदर्शः ॥
Why do we say अचि 'when a vowel follows'? Observe दर्श्श्यते ॥,