FOR

        [SIC\]FOR Loop_Variable n1 n2 n3 TO n4 BY n5 n6 TO n7
        or
        [SIC\]FOR /WHILE Logical_Expression

    Open a FOR-NEXT loop  to  be  executed  for  values  in  the  list  (FOR
    Variable),  or  until  a  logical expression becomes false (FOR /WHILE).
    The last character of the prompt becomes a ':' instead of '>',  and  all
    subsequent  commands typed in until  NEXT  are the body of the loop.  Up
    to nine loops may be nested in any way. The index of the  loop  will  be
    substituted  to  the  loop variable Loop_Variable during loop execution.
    The substitution occurs  also  within  character  strings  if  the  loop
    variable  name  is  included  between single quotes. Note that the index
    values may be real.

        [SIC\]FOR Loop_Variable n1 n2 n3 TO n4 BY n5 n6 TO n7

    The loop specified in this example will execute for the following values
    of the index :
            n1
            n2
            n3, n3 + n5, n3 + 2 n5, n3 + 3 n5, ... , n4
            n6, n6 + 1, n6 + 2, ... , n7
    (assuming that n4-n3 is a multiple  of  n5,  n7-n6  an  integer).   Loop
    variables  are  undefined  outside  the loop, and must not be previously
    defined. Invalid ranges are ignored  at  execution  time:  e.g.  in  the
    previous  example,  the loop would not be executed for n3 TO n4 BY n5 if
    n5*(n4-n3) < 0, but no error is signaled. Increments  of  0  produce  an
    error.

    Conditional loops execute until the logical  expression  becomes  false.
    For example FOR/WHILE .TRUE. will execute forever...