ख्यत्यात् परस्य

There is the substitution of उ for the अ of अस् of the Ablative and Genitive Singular after सखि and पति , when for the इ of those two stems य् is substituted.
The phrase ङसिङसोः and उत् are understood here also. The ख्य means and includes खि and खी when the इ is changed to य, and त्य denotes ति and ती, the इ being changed to य ॥ Thus सखि + अस् = सख्युः as सख्युरागच्छति, सख्युः स्वम् ॥ So also पत्युरागच्छति, पत्युः स्वम् ॥ The illustration of खी is सखी which is derived from the Denominative Verb thus : सहखेन वर्त्तते = सखः, सखमिच्छति = सख + क्यच् 3.1.8 = सखीय 7.4.3. Now by adding क्विप् to the denominative root सखीय we get सखीः 'one who wishes for a friend'. The Ablative and Genitive Singular of this word will be सखी + अस् = सख्युः also. Of ती we have the following example. लूनमिच्छति = लूनीय, add क्विप् = लूनीः, the Ablative and Genitive singular of which is also लून्युः, the न् of लूनी being the substitute of त् of Nishtha, is considered like त् 8.2.1. The peculiar exhibition of ख्य and त्य in the sutra, instead of saying directly सखिपतिभ्यां indicates that the rule does not apply to words like अतिसखि &c : where we have अतिसखेः, सेनापतेः ॥ The word अतिसखि is घि in spite of the prohibition (l. 4.7), for that prohibition applies only to सखि and not to a compound which ends in it, on the maxim ग्रहणवता प्रातिपदिकेन तदन्तविधिर्नास्ति ॥ "That which cannot possibly be anything but a Pratipadika does (contrary to 1.1.72) not denote that which ends with it, but it denotes only itself". According to Dr. Ballantyne this rule applies to all खी and ती, such as सुखीः 'one who loves pleasure' (सुखमिच्छति = सुखीय + क्विप्). and सुतीः 'one who wishes a son' (सुतमिच्छति = सुतीय + क्विप्): Thus सुख्युः, सुत्युः &c.