The Tantrāloka

"Light on Tantra" — thirty-seven chapters synthesising the Śaiva Tantric traditions of Kashmir into one non-dual system: consciousness contracting itself into every limited knower, the alphabet as the emanative structure of reality, and recognition (pratyabhijñā) as the whole of liberation.

The serious Tantra, and it is nothing like the popular version. Note the alphabet claim especially: the sounds are the mātṛkā, the little mothers, out of which the real is emitted. That is the Sefer Yetzirah's thesis, reached independently, in another alphabet.