UBT_bang_.html -- ACL2 Version 6.3

## UBT!

undo commands, without a query or an error

    Major Section:  HISTORY

    Example:
    :ubt! :x-4

The keyword command `:ubt!` is the same as `:``ubt`, but with related queries suppressed appropriately, and with a guarantee that it is ``error-free.'' More precisely, the value returned by `:ubt!` will always be of the form `(mv nil val state)`. `:``Oops` will undo the last `:ubt!`. See ubt, see ubu, and see u.