This repeatedly freezes the whole machine (a G5 quad), needing a power reboot. Welcome to Clozure Common Lisp Version 1.2-r9226-RC1 (DarwinPPC32)! ? (defun stress-test () (loop for n from 1 do (process-run-function (format nil "Stress ~D" n) #'(lambda () (loop do (1+ 1)))))) STRESS-TEST ? (stress-test)