REDEF!

system hacker's redefinition command
Major Section:  MISCELLANEOUS

Example and General Form:
ACL2 !>:redef!
ACL2 p!>
This command sets ld-redefinition-action to '(:warn! . :overwrite) sets the default defun-mode to :program, and invokes (set-state-ok t). It also introduces (defttag :redef!), so that redefinition of system functions will be permitted; see defttag. Finally, it removes as untouchable all variables and functions.

This command is intended for those who are modifying ACL2 source code definitions. Thus, note that even system functions can be redefined with a mere warning. Be careful!