Block

 Executes a block of statements if the logical expression is true.
 The block of statements starts immediately following the IF
 statement.  The block of statements can be followed by optional
 ELSE IF statements (any number) and one optional ELSE statement.
 The entire block IF construct must be terminated by an END IF
 statement.  Format:

    [name:] IF (e) THEN
      block
    [ELSE IF (e1) THEN [name]
      block]...
    [ELSE [name]
      block]
    END IF [name]

    name   Is the name of the IF construct.

    e,e1   Are logical expressions.

    block  Is a series of zero or more Fortran statements
           (called a statement block).

 If a construct name is specified in a block IF statement, the same
 name must appear in the terminal END IF statement.  If no construct
 name is specified in the block IF statement, no name can appear in
 the terminal END IF statement.  The construct name must be a unique
 identifier in the program unit.

                                NOTE

         No additional statement can be placed after the  IF
         THEN  statement  in  a  block  IF  construct.   For
         example, the following statement is invalid in  the
         block IF construct:

            IF (e) THEN I = J

         This  statement  is  translated  as  the  following
         logical IF statement:

            IF (e) THENI = J