GOSUB                    Execute Subroutine

 GOSUB {linenum1 | linelabel1}
 .
 .
 .
 RETURN [{linenum2 | linelabel2}]

    Causes program execution to branch to the specified line number or
    line label; when the RETURN statement is encountered, execution
    branches to the statement immediately following the most recent GOSUB
    statement--or to a specified line number or line label.

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      Notes:    Subroutines may be called any number of times, from any
                number of different points in a program. They may be
                nested, and they may have multiple RETURN statements.