plot3d (a[x]^2 - x[a]^3, [a[x], -1, 1], [x[a], -1, 1]); causes an error related to subscription variables.
This works for me using a fairly recent maxima and cmucl.
Hi, I have also confimed it works, buth with the latest git and the git four days ago. It seems I made some mistake here. Anyway, I close this one. Sorry...