+ ;; I think that a failure of this assertion means that we're
+ ;; trying to access a variable which was improperly closed
+ ;; over. The PHYSENV describes a physical environment. Every
+ ;; variable that a form refers to should either be in its
+ ;; physical environment directly, or grabbed from a
+ ;; surrounding physical environment when it was closed over.
+ ;; The ASSOC expression above finds closed-over variables, so
+ ;; if we fell through the ASSOC expression, it wasn't closed
+ ;; over. Therefore, it must be in our physical environment
+ ;; directly. If instead it is in some other physical
+ ;; environment, then it's bogus for us to reference it here
+ ;; without it being closed over. -- WHN 2001-09-29
+ (aver (eq physenv (lambda-physenv (lambda-var-home thing))))