Minus the seventh chord. According to the related information of chords, we know that 13+7 is minus seven chords. Minus Seventh Chord is abbreviated as Minus Seventh Chord or Minus Seventh Chord (to borrow the name in the mode). A third minor is superimposed on the MINUS triad, and the root and seventh tones form a MINUS seven interval. The structure of negative seven chords is: the root and three tones are small intervals, the three tones and five tones are small intervals, and the root to seven tones are negative seven degrees, which is customarily called "three plus three plus three plus three".