Infield Fly Rule Revisited

[DG]

I thought I understand but now I am confused.

First, IFF should require ordinary effort by an infielder, regardless of who caught the ball, or dropped it.

Second, if an IFF is dropped or let fall to the ground, the batter is still out. It is a live ball.

Third, if a ball that is in flight but not an IFF is dropped or let fall to the ground, then batter is out and ball is dead.

All of this prevents double plays that are not earned by the defense.