Showing research to professor who is not my advisor I am a PhD student in mathematics. I am going to participate in a conference. I want to show my research to some great mathematcian who is a specialist in the area that I am working on.

A friend of mine had a bad experience with showing her result to some great mathematician. In fact, she showed her result to the guy and he said that it was good and to keep up the good work, but two months later he put an article in arXiv and most of the parts of his article were as same as my friend’s. As such, I am bit scared to show my result to someone. On the other hand, I need to show my result to someone for completing a minor thing.

Does someone have any idea what I have to do?
First of all: you should really be asking your advisor this,  not strangers who don’t know your circumstances.

In any case: if you have a result that you feel is ready to be shown to others, why not write it up and put it on ArXiv yourself? That way no one could do this to you.