Hi! Using a vanilla "XEmacs 21.2 (beta35) \"Nike\" [Lucid] (i386-unknown-freebsd3.2) of Tue Sep 19\ 2000 on lycius.LF.net" I can dump core with (let ((str "as you like it")) (if (string-match "^.*$" str) (replace-match "\\U" t nil str))) The "\\U" might well be pretty dumb, but.. Lisp backtrace follows: # (unwind-protect ...) replace-match("\\U" t nil "as you like it") (if (string-match "^.*$" str) (replace-match "\\U" t nil str)) # bind (str) (let ((str "as you like it")) (if (string-match "^.*$" str) (replace-match "\\U" t nil str))) eval((let ((str "as you like it")) (if (string-match "^.*$" str) (replace-match "\\U" t nil str)))) # bind (expr) eval-interactive((let ((str "as you like it")) (if (string-match "^.*$" str) (replace-match "\\U" t nil str)))) # bind (standard-output opoint ignore-quotes # eval-last-sexp-arg-internal) eval-last-sexp(t) # bind (standard-output) #<compiled-function nil "...(13)" [standard-output terpri #eval-last-sexp t] 2 959532 nil>() call-interactively(eval-print-last-sexp) # (condition-case ... . error) # (catch top-level ...) #0 0x284d3c78 in kill () from /usr/lib/libc.so.3 #1 0x80b1983 in fatal_error_signal (sig=6) at emacs.c:514 #2 0xbfbfdfdc in ?? () #3 0x80b490a in assert_failed (file=0x8247ee6 "lisp.h", line=1128, expr=0x8247f00 "RECORD_TYPEP (obj, lrecord_type_string)") at emacs.c:3135 #4 0x819f408 in Freplace_match (newtext=136980484, #fixedcase=136980508, literal=136980484, string=140433620, strbuffer=136980484) at lisp.h:1128 #5 0x80ba2de in Feval (form=139636672) at eval.c:3331 #6 0x80b54f8 in Fif (args=139664768) at eval.c:691 #7 0x80ba153 in Feval (form=139664636) at eval.c:3304 #8 0x80b6029 in Flet (args=139664444) at eval.c:775 #9 0x80ba153 in Feval (form=139706220) at eval.c:3304 #10 0x80bacf7 in Ffuncall (nargs=2, args=0xbfbfcdf4) at eval.c:3528 #11 0x808f74e in execute_optimized_program ( program=0x8699990 "\b