Logical expressions can contain one or more logical operators and
  logical, integer, or relational operands.  The following are
  logical operators:

     Operator  Meaning
     ---------------------------
     .AND.     Logical conjunction: the expression A .AND. B
               is true if both A and B are true.

     .OR.      Logical disjunction (inclusive OR):  the ex-
               pression A .OR. B is true if either A, B, or
               both, are true.

     .XOR.     Same as .NEQV.

     .NEQV.    Logical inequivalence (or exclusive OR): the
               expression A .NEQV. B is true if either A or
               B is true, but false if both are true.

     .EQV.     Logical equivalence: the expression A .EQV. B
               is true if both A and B are true, or both are
               false.

     .NOT.     Logical negation: the expression .NOT. A is
               true if A is false and false if A is true.