I wondered why I couldn’t get a IF-sentence to work in CAS-view, and found out that the following simple IF-sentence combinations doesn’t work in CAS-view.
1.
c = “+”
T = “(a + b)”
$1 = a
$2 = T
$3 = If[ IsEqual[ c, “+” ] == true, $1 * $2, If[ IsEqual[ c, “-“ ] == true, $2 - $1 ] ]
This input can’t be used.
But this work:
$3 = $1 * $2
$3 = $2 - $1
2.
d = “a”
c = “+”
T = “(a + b)”
$1 = T
$2 = If[ IsEqual[ c, “+” ] == true, d * $1, If[ IsEqual[ c, “-“ ] == true, $1 - d ] ]
This input can’t be used.
But this work:
$2 = d * $1
$2 = $1 - d
I need to use those kinds of IF-sentences in CAS-view when the students use a dropdown-menu to choose the kind of operation they would like to use to isolate a letter in a formula and also get a description shown in text that describes what have been done and to get the formulas written in a table where they are aligned by their equal sign.
The same problem 
1) please always post your .ggb file
2) IsEqual() isn't a CAS command so there's no point using it there instead of the Algebra View - you can use == instead
3) There's no point using the CAS for checking Strings anyway, just make sure it has a label and you can do
or (more robust)in the Algebra View
I have been doing some tests
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