Is there a way to see if two accounts are the same? (I found some related questions on meta but not enough information)
Perhaps stackexchange uses some known techniques to calculate the probability that two accounts are the same (using cookies, source ip address, HTTP headers, ...)? (obviously these techniques can be fooled or can lead to wrong results, but in some cases they can be useful)
For example yesterday I answered an homework-style question Proof for ACYCLIC PARTITION being NP-complete (in the original formulation I thought that it was a completely different problem) and today I see a question by a new user that has a very-very similar formulation: https://cstheory.stackexchange.com/questions/21334/np-complete-proof-for-multiple-choice-matching
I think that the site should be tolerant in similar cases, but it could be useful to avoid spammers and disturbers (especially in other stackexchange sites that have a larger number of users).