After the name of a subject of commentary an affix comes in the sense of 'its commentary', as well as in the sense of 'what occurs there'.,
That by which a thing is explained is called व्याख्यान or 'commentary'. The name of a thing explainable is called व्याख्यातव्यनाम ॥ After such a name, being in the 6th case in construction, the affix is added. The affix means तस्यव्याख्यानं as well as तत्रभव, the latter being read into the sutra by virtue of च ॥
Thus सुपां व्याख्यानः = सौपो ग्रन्थः 'Saupa, a book on the explanation of case-affixes'. So also 'Tainga-- a Commentary on Verbal affixes' कार्तः 'Karta-- a Commentary on krit affixes'. सौप &c. may also mean सुप्सु भवं &c.
Why do we say व्याख्यातव्यनाम्नः 'after the name of the thing explainable'? The thing to be explained must be a Book, therefore, the affix will not apply to the name of a city &c. For example, if a model be made to describe the city of Pataliputra, such a model will not be named after Pataliputra by the addition of affix. Thus सुकोशला is a modal giving a description of Pataliputra. This will not be called Pataliputram.
The anuvritti of भव and व्याख्यान runs simultaneosly in all the subsequent apavada sutras, and hence we have read the anuvritti of भव into this sutra also.,