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[bbartlog]

Fold preflop.

You don't specify whether the third person to see the flop is still to act. I'm going to assume they folded or are otherwise irrelevant, but in reality it might matter...

I think I would call. If SB is doing a naked ace bluff (or any other kind of bluff), he will fold to a raise, but may fire again on the turn if we just call. I'm comfortable assigning him a > 50% chance of not having the nut flush here, and calling down on later streets.