“…Operads. Operads originated in algebraic topology [16,63] and, while they continue to be very important in that area (see, e.g., [11,28,29,65]), they have found applications in several other branches of mathematics, including geometry [35,43], algebra [57,64], combinatorics [3,56] and category theory [4,7,54]. Recently, operads have started to be considered also in theoretical computer science [23].…”