docs: function distances (tonic, gamut) {
    if (!tonic) {
      if (!gamut[0]) return []
      tonic = gamut[0]
    }
    tonic = op.setDefaultOctave(0, tonic)
    return gamut.map(function (p) {
      return p ? op.subtract(tonic, op.setDefaultOctave(0, p)) : null
    })
  }