@reid, thanks but maybe something more conclusive can be said. What if the contributer remains anon ? for instance, should i be citing kittykat at mathoverflow provided the solution to xxx in claim Y ? Or simply, the problem was mentioned and resolved at MO [see site ...]. In case that the person has a name and identity and which happens to be in one to one correspondence with real life, shouldnt i not just mention person blahblahblah helped me on this. See the point here again is a different one. It's somewhat analogues to me using Sage in my paper unless my computation heavily relies on it,.