A logical constant represents only the logical values true or
  false.  It takes one of these forms:

    .TRUE.[_k]
    .FALSE.[_k]

    k   Is an optional kind type parameter (1 for
        LOGICAL(KIND=1), 2 for LOGICAL(KIND=2), 4 for
        LOGICAL(KIND=4), and 8 for LOGICAL(KIND=8)).
        It must be preceded by an underscore (_).

  The type specifier for the logical type is LOGICAL.

  If a kind type parameter is specified, the logical constant has the
  kind specified.  If no kind type parameter is specified, the kind
  type of the constant is default logical.

  Note that logical data type ranges correspond to their comparable
  integer data type ranges.  For example, the LOGICAL*2 range is the
  same as the INTEGER*2 range.