Then I will give a complete answer.

Playing with one hand and aligning it up and down is called harmony, and if it is not in the music, it is called harmony interval.

Inheritance is another matter. Heritage linked. There is another knowledge point: Legacy connects two identical sounds, which means to play the full duration of the two sounds without disconnecting. Connecting two different voices means coherence.

PS: second floor ... children who have gone astray ...

Chords are three notes. Three notes played together are called column chords, and those played separately are called melody chords.