Assertion: concertina's button | /r/HasProperty | arranged in pair
Facets:
value: most commonly
type: DEGREE
value: with one button of a pair
type: OTHER
Source sentences:
text: The buttons on the bass-side keyboard are most commonly arranged in pairs, with one button of a pair sounding the fundamental of a chord and the other the corresponding major triad (or, sometimes, a minor triad).