This error message is unexcusably bad.
Error: The variable $FEATURE is unbound.
Fast links are on: do (si::use-fast-links nil) for
Error signalled by MACSYMA-TOP-LEVEL.
Broken at MACSYMA-TOP-LEVEL. Type :H for
Maxima should point out that "d" is not defined so
that the user can correct his expression to