Suppose, in my research (mathematical) I have a critical step that I need to solve, and, due to various reasons I cannot find decent answer to that step by myself or by contacting friends or colleagues, so that I decide to post a similar but simpler problem to the relevant StackExchange (Math). Now, if someone comes up with a good answer that I can use to further my research, will it be enough to acknowledge the contribution of the author of the answer and citing that particular thread of StackExchange, or do I need to include that person as a coauthor of the paper that I might prepare based on that answer?
I emphasize here that the paper is supposed to be not all about that particular result, there are many other things, and that particular answer is useful, albeit critically, at an intermediate stage of proving some results in the paper. I personally feel that citing and acknowledging the contribution is respectful enough. However, I want to know what the standard norm is.