[great-users] Smart way to ensure 1 and only 1 object?

[Gabriele Trombetti]

I have to do many times the following operation: make sure that exists 
exactly one object with certain carachteristics.
Is there a smart way to do that?

Seems to be a pain in GReAT... what I'm currently doing is:

If there are none, create one (needs 1 test, 2 cases, and one 1 rule for 
creation)
If there are multiple, delete all except one (needs 1 rule if my 
approach is correct... I will send another email regarding this).

Is there any way to do that with less than 5 blocks+rules?