Natyashastra
कोणं वा सप्रतिद्वारं द्वारविद्धं न कारयेत् । कार्यः शैलगुहाकारो द्विभूमिर्नाट्यमण्डपः ॥ ८०॥
The corner or a doorway should not be constructed with a direct opening. The ideal design for the stage should resemble a mountain cave with two levels.
english translation
koNaM vA sapratidvAraM dvAraviddhaM na kArayet । kAryaH zailaguhAkAro dvibhUmirnATyamaNDapaH ॥ 80॥
hk transliteration by Sanscript