/UNDEFINE

Use the /UNDEFINE directive to indicate that a condition is no longer defined.

Start of change /UNDEFINE must be followed by at least one space, and then the condition-name must be specified on the same line. The remainder of the line must be blank. End of change

Start of change In fixed-form, /UNDEFINE must begin in column 7. End of change

Start of change /UNDEFINE cannot be specified within a free-form statement. However, between free-form statements, /UNDEFINE can begin in column 7 or later. End of change

The /UNDEFINE directive removes a condition-name from the list of currently defined conditions. A subsequent /IF DEFINED(condtion-name) would be false. A subsequent /IF NOT DEFINED(condition-name) would be true.
Note: Any conditions specified on the DEFINE parameter will be considered to be defined when processing /IF and /ELSEIF directives. These conditions can be removed using the /UNDEFINE directive.