wxmaxima loop control query




I copied the following code from a tutorial
on Maxima, and find that it does not wotk with
wxMaxima:
"FOR A:-3 THRU 26 STEP 7 DO LDISPLAY(A)$"
I get  the error :
"(%i1) FOR A:-3 THRU 26 STEP 7 DO LDISPLAY(A)$
Incorrect syntax: a is not an infix operator
FORSpaceA:"
Am I doing something wrong?
Thanks
Carl David
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