In former times (with older scopes) I got for the SELECT? all active channels<1 to 4> and maths<1 to 4>. Now its DISPLAY:GLOBAL:CHN<x>:STATE? which returns the status for the chns but not for DISPLAY:GLOBAL:MATH<x>:STATE? which gives me a timeout after some seconds for inactive math. Why not simply get "0" ?. I don't want to handle timeouts!
There is also a compatibility mode to support SELECT? commands, but does not give any math channels back.
What is the Tektronix way to get the list of active channels?

Regards