701.37a To exert a permanent, you choose to have it not untap during your next untap step.

Is the result of choosing to exert a permanent, to have it not untap during your next untap step?

Or is the result of choosing to exert a permanent, to choose to have it not untap during your next untap step?

With respect to 502.2, the active player determines which of the permanents he controls untap. On occasion, the player is given a choice to not untap a permanent in that determination (eg. Vedalken Shackles).
Is exert giving that choice, but indicating the player must choose not to untap it?
Or is it just saying, it doesn't untap?

Why might this matter?

I steal my opponent's Glorybringer with Act of Treason. My opponent also controls Prophet of Kruphix.

I attack with and exert Glorybringer. It returns to my opponent. What he does with it on his turn isn't relevant.

On my next turn, do I get to choose for my opponent's Glorybringer in the determination of which permanents untap on my untap step and have it not untap?
Or does it get to untap because the rules only allow me to choose for the determination of permanents that I control and I don't control Glorybringer?
Or does it just not untap because it was exerted on my last turn and there's no choice involved in the result?
Or is there another possibility that I haven't considered?


Edit: It seems I got some clarification from Eli in this thread (https://www.reddit.com/r/magicTCG/comments/6831on/amonkhet_update_bulletin_rules_changes/)

Eli Shiffrin: “The choice is made at the time you exert it.”

This seems to imply that the third possibility is the result - it just doesn't untap because it was exerted on my last turn and there's no choice involved in the result.

Edited Todd Bussey (May 3, 2017 03:41:51 PM)