Natyashastra
ज्ञेयो वै वर्धमानस्तु हंसपक्षो पराङ्गमुखौ । जालवातायनादीनां प्रयोक्तव्यो विघाटने ॥ १६०॥
Vardhamāna is to be known as the Haṃsapakṣa (swan’s wing) gesture turned outwards; it should be used for representing the opening of lattice windows and similar objects.
english translation
jJeyo vai vardhamAnastu haMsapakSo parAGgamukhau । jAlavAtAyanAdInAM prayoktavyo vighATane ॥ 160॥
hk transliteration by Sanscript