瑜伽師地論略纂 2.20

2.20

Among the four kinds of obstacles, "obstacle of coverage" refers to houses, buildings, and so forth. "Obstacle of concealment" refers to supernormal powers, medicinal herbs, and so forth, concealing something so it cannot be seen. "Obstacle of overpowering" refers to being overpowered by superior force, namely sunlight and the like overshadowing the light of stars, fire, and so forth. "Obstacle of illusion" refers to various illusory obstacles caused by ghosts, spirits, incantations, and so forth.