How to make 'IF's in grasshopper

[Leeeees]

Hi.

I want to make an arch as an output, out of a gap between two circles. But there’s an error when the gap between the circles is 0. So I want to seperate the command like below.

Could anyone help?

Thanks in advance.

baeryum_ing.gh (354.5 KB)

[HS_Kim]

In that kind of situation, you could use Stream Gate.

baeryum_ing_re.gh (352.5 KB)