L     R     L
◦     ◦     ◦
◦     U     ◦  deactivated state
◦           ◦
O           O

L—————R ◦ ◦ L
•     •     ◦
•     U     ◦  activated by left button
•    |||    ◦
O     H     O

L ◦ ◦ R—————L
◦     •     •
◦     U     •  activated by right button
◦    |||    •
O     H     O