Fifty users on MO are identified simply by the name Andrew (with a capital A). Perhaps there are even more common names. Most websites require prospective users to register a name distinct from that of any existing user, so that all usernames are unique, but this does not appear to be so on MO. Why?

  • $\begingroup$ Indeed, it seems that there are usernames more frequent than Andrew, here is a SEDE query listing the most frequent ones. The duplication goes down if you look at users with non-negligible reputation, here are the results if you take reputation at least 102 or at least 1000. $\endgroup$ Commented Jul 11, 2020 at 8:30
  • $\begingroup$ Here is a query which can be used to list all users name Andrew, Adam or any other username you want to try. $\endgroup$ Commented Jul 11, 2020 at 8:32
  • $\begingroup$ Usernames are unique. The names that users choose to display, however, are not. (As one of the horde of Andrews, I feel the need to reply! Btw, I count 53 members of this distinguished horde.) $\endgroup$
    – Andrew
    Commented Jul 14, 2020 at 7:22
  • $\begingroup$ @Andrew It is interesting that we each get somewhat different counts. I get 66 Andrews and 70 if I count case insensitive. (There are four lowercase answers.) $\endgroup$ Commented Jul 15, 2020 at 4:54
  • $\begingroup$ Maybe difference depends on whether we count unregistered users? (I.e., the users who participated here without registering, just relying on their login being remembered in cookies.) $\endgroup$ Commented Jul 15, 2020 at 4:55
  • $\begingroup$ A few months ago, there was a flood of "Reinstate Monica" usernames. No one was against this, but the irony was when several Reinstate Monica s where commenting on the same post. Because if you wanted to answer one of them by mentioning, it would have ended in a headache. $\endgroup$
    – polfosol
    Commented Jul 18, 2020 at 10:05

2 Answers 2


MathOverflow has been part of the Stack Exchange network for a very long time, and the Stack Exchange network doesn't enforce this. (I'm not sure how it was back in the days.)

Just as in real life, several people can go by the same first and last name. This usually doesn't cause any problem; it only gets confusing when they interact (but that can be funny too sometimes). You only interact with users here if they're part of the same Q&A 'thread' in the form of answers or comments.

Related question on Meta Stack Exchange: Why does Stack Overflow allow duplicate display names?


It should be noted that one is allowed to change the display name at will. (This has caused some problems; I have seen the downside of being impersonated in this way.) Indeed, many of the display components of the platform are meant to be configurable.

Gerhard "Let Us All Become Andru" Paseman, 2020.07.10.

  • 4
    $\begingroup$ There are still two users here named "Gerhard Paseman". But it looks like they are the same person... $\endgroup$ Commented Jul 11, 2020 at 11:45
  • 5
    $\begingroup$ Two? There should be five or six. Gerhard "Need To Check On Myself" Paseman, 2020.07.11. $\endgroup$ Commented Jul 11, 2020 at 16:54

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