An array of six integers representing the ic (interval class) content of a chord, where the first digit indicates the number instances of IC1 in the set, the second, IC2, third, IC3, fourth, IC4, fifth, IC5, and sixth, IC6. For example, is the ic vector for a major triad, showing that it contains zero IC1 (semitones), zero IC2 (wholetones), one IC3 (minor 3rd), one IC4 (major 3rd), one IC5 (perfect 4th), and zero IC6 (tritones). Identity of interval vectors (when two sets have the same IC vector) is the determinant Forte used for his equivalence relations between pc sets (transposition, inversion, Z-relation).