Hey I am wondering where 5PM is? I enjoyed reading his posts on partial differential equations and am just curious.
The account seems to be deleted.
Just for references to answer zyx's concern.
user53153 + key word site:math.stackexchange.com will give you 5pm's posts.
Use this StackExchange data query, just type 5pm's username placeholder
user53153 into the parameter box and hit enter, you will get all the answers by 5pm.
Also there are several users that answer question like 5pm (yet there is no direct evidence showing they are 5pm, or a mimicking persona created by 5pm's admirers).
These users show superb familiarity with various literature of different branches of analysis (complex, real, harmonic, pde, etc), as well as a great amount of knowledge of the StackExchange site itself (even more than moderators), like to answer old questions nobody would ever care, offer bounty to old tumbleweed questions, and use up their daily vote limit to remove questions from the unanswered queue.
Some of these users never logged back in MSE again after a short period amount of active participation.