तत्र विदित इति च

Operational rule vidhi

To the same bases सार्वभूमि and पृथ्वी , being in the 7th case in construction, are added the same affixes अण् and अञ् respectively, in the sense that of 'known therein'.

Word by word (padaccheda)

Indeclinable तत्र avyayaSubstitute / term विदितः prathamā · ekavacanaIndeclinable avyayaIndeclinable च avyaya

Indeclinable An avyaya such as च "and", वा "optionally", न "not".
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.

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Full reading

तत्र विदितः च

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

Commentary

To the same bases सार्वभूमि and पृथ्वी , being in the 7th case in construction, are added the same affixes अण् and अञ् respectively, in the sense that of 'known therein'.
The word विदितः means known published &c. सर्वभूमौ विदितः = सार्वभौमः known in the whole world. So also पार्थिवः ॥

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.