Reference: leviCivita

leviCivita(a1, a2, ..., aN) returns 1 if (a1, a2, ..., aN) is an even permutation of the N first positive integers, -1 if (a1, a2, ..., aN) is an odd permutation of the N first positive integers, and 0 otherwise. Every ak must be an integer between 1 and N.