Laghusiddhāntakaumudī.
This text is an abridgement by Varadarāja of an earlier work, the Siddhānta Kaumudī of Bhaṭṭoji Dīkṣita.
The reference text used by Medhā Michika is the "Gītā Press" edition.
A digital version of this can be found at archive.org:
Ballantyne made a translation into English of this text in the mid-nineteenth century. A digital version of this can be found at archive.org: