I just noticed (by looking at my reputation) that I accidentally downvoted the following answer:
Oscillation of the summatory Möbius function
This was (probably) because I was reading the question in my tablet computer (not the best one in the market), and I wanted to upvote that answer, but accidentally pressed the downvote button with my stupid finger. I tried to upvote it now, but the system tells me that, since 20 hours have passed, my vote is locked.
Is there any way to reverse this error of mine?