This is SBCL 2.0.4.debian, an implementation of ANSI Common Lisp.
More information about SBCL is available at <http://www.sbcl.org/>.

SBCL is free software, provided as is, with absolutely no warranty.
It is mostly in the public domain; some portions are provided under
BSD-style licenses.  See the CREDITS and COPYING files in the
distribution for more information.
* (sb-ext::without-package-locks (defun sb-impl::output-float-infinity (x stream) (print-object x stream)))

debugger invoked on a PACKAGE-LOCKED-ERROR in thread
#<THREAD "main thread" RUNNING {1000580083}>:
  Lock on package SB-IMPL violated when interning OUTPUT-FLOAT-INFINITY while
  in package COMMON-LISP-USER.
See also:
  The SBCL Manual, Node "Package Locks"

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [CONTINUE      ] Ignore the package lock.
  1: [IGNORE-ALL    ] Ignore all package locks in the context of this operation.
  2: [UNLOCK-PACKAGE] Unlock the package.
  3: [ABORT         ] Exit debugger, returning to top level.

(PACKAGE-LOCK-VIOLATION #<PACKAGE "SB-IMPL"> :SYMBOL NIL :FORMAT-CONTROL "interning ~A" :FORMAT-ARGUMENTS ("OUTPUT-FLOAT-INFINITY"))