UBU.html -- ACL2 Version 6.3

## UBU

undo the commands back up to (not including) a command descriptor

    Major Section:  HISTORY

    Examples:
    :ubu :x-3      ; undo the last three commands (same as :ubt :x-2)
    :ubu (:x -3)   ; same as above
    :ubu fn        ; undo back up to, but not including the introduction of fn
                   ; (so fn will continue to be defined)
    :ubu 5         ; undo back up to, but not including, the fifth command
                   ; executed (leaving the first five commands in place)

See command-descriptor.

`Ubu` takes one argument, a command descriptor, and undoes the commands from `:``max` (aka `:x`) up to, but not including, the indicated command. See command-descriptor.

`Ubu` can cause errors or queries. To avoid these, see ubu!.

Also see ubt, which is similar but also undoes the indicated command. As for `:``ubt`, `:``oops` will undo the undo (see oops) and `ubu` will not undo into ``prehistory''.

See u for how to undo just the latest command, and see ubt and see ubt! for how to undo back through (that is, including) the current command.