Major-chord progressions are constructed in the harmonization of major scales in triads. The Petrushka chord is defined as two simultaneous major triads separated by a tritone. The riff uses of triads, particularly second inversions. The main chord pattern of the song alternates between B major and D minor triads. Minor chords are constructed by the harmonization of minor scales in triads. Standard tuning requires four chord-shapes for the major triads. Both major and minor chords are examples of musical "triads", which contain three distinct notes. It occurs above the root of all major and minor chords (triads) and their extensions. The voices sing a motif of descending triads. They have ties with the bikies and triads. They cooperate with the police to impede the expansion of triads and other organized gangs. Active site cysteine residues are the functional unit in cysteine protease catalytic triads. There are four "basic triads" (major, minor, augmented, diminished). Examples are especially prevalent for derivatives of the cobalt and nickel triads. Western music is based on major and minor triads.