bāhyābhyantarastambhavṛttir deśakālasaṃkhyābhiḥ paridṛṣṭo dīrghasūkṣmaḥ [YS 2.50]

yatra praśvāsapūrvako gatyabhāvaḥ sa bāhyaḥ. yatra śvāsapūrvako gatyabhāvaḥ sa ābhyantaraḥ. tṛtīyaḥ stambhavṛttir yatrobhayābhāvaḥ sakṛṭprayatnād bhavati. yathā tapte nyastam upale jalaṃ sarvataḥ saṃkocam āpadyate tathā dvayor yugapad gatyabhāva iti. trayo 'py ete deśena paridṛṣṭā iyān asya viṣayo deśa iti. kālena paridṛṣṭāḥ kṣaṇānām iyattāvadhāraṇenāvacchinnā ity arthaḥ. saṃkhyābhiḥ paridṛṣṭā etāvadbhiḥ śvāsapraśvāsaiḥ prathama udghātas tadvan nigṛhītasyaitāvadbhir dvitīya udghāta evaṃ tṛtīyaḥ. evaṃ mṛdur evaṃ madhya evaṃ tīvra iti saṃkhyāparidṛṣṭaḥ. sa khalv ayam evam abhyasto dīrghasūkṣmaḥ.