@NotNull
    private ScrollHelper create(@NotNull ThreeSide master, @NotNull ThreeSide slave) {
      assert master != slave;
      assert master == ThreeSide.BASE || slave == ThreeSide.BASE;

      boolean leftSide = master == ThreeSide.LEFT || slave == ThreeSide.LEFT;
      SyncScrollable scrollable = leftSide ? myScrollable12 : myScrollable23;

      Side side;
      if (leftSide) {
        // LEFT - BASE -> LEFT
        // BASE - LEFT -> RIGHT
        side = Side.fromLeft(master == ThreeSide.LEFT);
      }
      else {
        // BASE - RIGHT -> LEFT
        // RIGHT - BASE -> RIGHT
        side = Side.fromLeft(master == ThreeSide.BASE);
      }

      return new ScrollHelper(myEditors, master.getIndex(), slave.getIndex(), scrollable, side);
    }
@NotNull
    private ScrollHelper create(@NotNull ThreeSide master, @NotNull ThreeSide slave)