The use of atomic weapons at the end of World War 2 fostered fears about their potential use during the Cold War years.
Interrupts and signals are low-level mechanisms that can alter the flow of control in a way similar to a subroutine, but usually occur as a response to some external stimulus or event (that can occur asynchronously), rather than execution of an 'in-line' control flow statement.
Put data records that are to be processed as part of the )IF or )ELSE on the next input record. The control-statement is optional on the same line as either the )IF or )ELSE control words, but a valid statement must be supplied for an )IF and )ELSE control statement before the end of the skeleton member.