परि+करोति किं रूपम्?

परि+करोति किं रूपम्? इति विचार्यते। परि+करोति किं रूपम्? इति विचार्यते। If the root कृ preceded by prefixes सम्, परि, and उप (सम्पर्युपेभ्यः करोतौ भूषणे ६-१-१३७), it will get additional letter स् (सुट्) before the root कृ and after the prefix परि. So now we get परि+स्+करोति। At this stage, the rule परिनिविभ्यः सेवसितसयसिवुसहसुट्स्तुस्वञ्जाम् (८-३-७०) is applied, under which the letter स् is replaced by the letter ष्। Now we get परि+ष्+करोति=परिष्करोति।

In लट्-लकार it is OK. But लङ् etc., what would be the form of कृ if preceded by the prefix परि? For example if we take लङ्, the position would be परि+अ (अट्)+स् (सुट्)+कृ। Here, परि is not immediately followed by स्, there is another letter between परि and स् before कृ । Here another rule applies that is सिवादीनां वा अड्व्यवाये ऽपि (८-३-७१)।  As per this rule परि if followed by स्, even if there is an intervention of letter अ (अट्), the letter स् will be replaced by the letter ष् optionally. So, we get two forms via परि+अ+ष्+करोत् and परि+अ+स्+करोत्।  If you combine this as per सन्धि rule, you will get पर्यष्करोत् and पर्यस्करोत्॥

  

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