How can I define custom symbols with variants?

Questions
1

I want to use the symbol plus.o and its variant plus.o.big as one symbol dsum with variant dsum.big.

I feel like this could be accomplished with the symbolx package… but I can’t get it to render the dsum.big correctly.

Does anyone have any non-complicated suggestions? Thanks!

2

Can you describe a bit more what doesn’t work, and what code you have tried? It’s easier for us to help if we see what you have, and how it differes from what you want.

To post your code, check out How to post in the Questions category