I am currently taking a math class and saw that a professor from a different university had some ideas/open questions for final course research projects on his page. I began working on one of these project ideas but I ran into a problem that I couldn't overcome (basically a certain type of equation doesn't seem to exist for the object proposed in his question).
I asked my math professor about it but they weren't sure. Would it be inappropriate to email the professor from a different university about it and ask them if this is the correct direction to work in for the problem? It would just be a one time email, not like expecting him to answer all my questions, but I understand how he could take it as such.