There is a coworker who has stolen credit for my work. I created a system that will show live statuses of printing machines throughout the plant. There was one glitch in it so the coworker made an improvement and then re-wrote the entire system (copying 90% of my code, yet he added a new piece of hardware then took over the project). Now he asks me programming questions from time to time. I don't mind teaching coworkers how to program, but since he has stolen my ideas and credit in the past I am reluctant to teach him all I know. Today he asks me for a particularly challenging algorithm for this system. His code now looks exactly like the way I would program! How would you handle the situation? How can I decline helping him without appearing to not being a team player?