Defined_Operations

 A defined operation is unary or binary.  It is defined by a
 function subprogram containing a generic interface block with the
 specifier OPERATOR.  A defined operation is not an intrinsic
 operation.  However, you can use a defined operation to extend the
 meaning of an intrinsic operator.

 For defined unary operations, the function must contain one
 argument.  For defined binary operations, the function must contain
 two arguments.

 Interpretation of the operation is provided by the function that
 defines the operation.

 A Fortran 95/90 defined operator can contain up to 31 letters, and
 is enclosed in periods (.).  Its name cannot be the same name as
 any of the following:

   o The intrinsic operators  .NOT., .AND., .OR., .XOR., 
     .EQV., .NEQV., .EQ., .NE., .GT., .GE., .LT., and .LE.

   o The logical literal constants .TRUE. or .FALSE..

 No two intrinsic operators can follow one another, but an intrinsic
 or binary operator can be followed by a defined unary operator.

 The result of a defined operation can have any type.  The type of
 the result (and its value) must be specified by the defining
 function.

 The following examples show expressions containing defined
 operators:

   .COMPLEMENT. A

   X .PLUS. Y .PLUS. Z

   M * .MINUS. N