Car cost - http://www.cs.cmu.edu/afs/cs.cmu.edu/project/clisp/src/beta/compiler/represent.lisp

http://www.cs.cmu.edu/afs/cs.cmu.edu/project/clisp/src/beta/compiler/represent.lisp
... values arg-p (1+ n) nil (car costs) (car load) (not (and (equalp ccosts (car costs)) (equalp ... when (eq op ref) (add-costs (car cost)) (return) (undefined-value)) ;;; SELECT ...
Source: www.cs.cmu.edu