a surface), and some point in it, and all the loops both starting and ending at this point — paths that start at this point, wander around and eventually return to the starting point.
به زبان دیگر هر عضو formula_21 یک مجموعه formula_23 است کهformula_24 یک دور روی نقطه formula_3 وformula_26 که منظور از formula_27 این است که دو دور formula_24 و formula_29 هموتوپ هستند.