@Alejandro Jakubi 

The online documentation seems more complete than the built in one I was using. Thanks again for your help!

@Alejandro Jakubi 

The online documentation seems more complete than the built in one I was using. Thanks again for your help!

Thanks very much for your answer! You're right I meant inert sum instead of indefinite sum. In fact I don't need the conditional part but it's nice to know I can do things like this.

Your code works but I couldn't quite understand it. I can't find the conditional statement in the help, and I don't understand your use of the % symbol. Also, it seems I need to expand() the result to get back the sigma expression.

Thanks very much for your answer! You're right I meant inert sum instead of indefinite sum. In fact I don't need the conditional part but it's nice to know I can do things like this.

Your code works but I couldn't quite understand it. I can't find the conditional statement in the help, and I don't understand your use of the % symbol. Also, it seems I need to expand() the result to get back the sigma expression.