Mu.

https://en.m.wikipedia.org/wiki/Mu_(negative)

See Non-dualistic meaning section.

Depends on what kind of sandwich it was before, and along which axis you cut it, and where you fall on the sandwich alignment chart.

Assuming a normal cut, this isn't a question about how you define a sandwich, this is a question about the number of servings, and only you can answer that.

Yes, you do have one or two sandwiches.

Edit: oh dang, I wanted to make the “or” joke so badly that I missed the option to have zero sandwiches.