According to the opinion of Northern Grammarians i is not substituted for that a which is obtained by shortening the long ā of the feminine (under sūtra ke'ṇaḥ [[7.4.13]] before the affix ka) which is preceded by y or a k,
The mention of 'northern grammarians' makes this an optional rule. As इभ्यका or इभ्यिका, क्षत्रियका or क्षत्रियिका, चटकका or चटकिका, मूषिकका, मूषिकिका ॥ Why do we say preceded by य् or क् ? Observe अश्वक-अश्विका only (from अश्वा) ॥ The word यकपूर्वायाः is exhibited in the feminine, in order to indicate that the rule applies when the feminine affix आ is shortened to अ ॥ Therefore not here शुभंयिका from शुभंया (शुभं याति). So also भद्रंयिका from भद्रया, where आ is part of the root या (see 3.2.74).
Vart:- Prohibition must be stated of the य् and क् being finals of a root. When the य् or क् preceding this अ, is the final of the root, the prohibition contained in the sutra, does not apply: as सुनयिका, सुशयिका, and अशोकिका ॥
Why do we say 'of long आ'? Observe सांकाश्ये भवा = सांकाश्यिका ॥ The word संकाश्य is formed from संकाश by the affix ण्य (संकाशे निर्वृत्तं) ॥ Then is added the affix वुञ् 4.2.121. Here there is no shortening of a long आ, and hence no option is allowed. But in इभ्यका or इभ्यिका the long आ has been shortened. Because this word is thus derived: इभमर्हति = इभ्या (दण्डादिभ्योयः (V. I. 66)). To this क is added, and the long आ is shortened.
Why is the word स्थान used in the sutra, when by the general rule षष्ठी स्थाने योगः this word would be understood here? The special mention is for the sake of pointing out that the अ which takes the place of आ is intended here: i. e. the इ replaces this short अ; but had the word स्थाने not been used in the sutra the इ would have replaced the long आ ॥,