suggestion: identify defined variables ( in cas )

[Angus]

hi again,

I'd like to excuse myself for the mass of questions I asked during the last days.
I try to play with the prime as often as possible. During breaks and in the evening.
I hope a lot that this device will be like a helpful friend one day. As opposed to the thing it is up to now. I mean it is hard enough to do re-calculations of known things. I can't even think about unknown or new stuff right now.

Being in cas mode I tried something like:

solve( { x^2+a/b=0 , b*x=1 } , { a, x } ) results in {[-1/b 1/b]}

whereas solve( { x^2+a/b=0 , b*x=1 } , { b, x } ) gives [[]]

First I was perplexed but then I looked at the mem-viewer and found a list 'a' defined in cas. I have no idea what was in there nor when I stored it, because when I tried to look at it the prime kept rebooting. After deleting that list

solve( { x^2+a/b=0 , b*x=1 } , { b, x } ) results in {[-1/a -a]}


What do you guys advise students how to avoid such traps. If you don't know a priori what to expect you easily get fooled by the system I guess.
Would it be an option to print defined Variables in capitalized letters? In home and apps things could be similar I guess. I only did calculations in home so no problems there.
But having learned that programs are compiled as being in home that troubles me though.

cheers