4.1.4 Logical Expressions  A logical expression consists of one
or more logical operators and logical, numeric, or relational
operands. The following are logical operators:  Operator 
Example  Meaning  .AND.  A .AND. B   Logical conjunction: the
expression is true if both A and B are true.  .OR.  A .OR. B  
Logical disjunction (inclusive OR): the expression is true if
either A, B, or both, are true.  .NEQV.  A .NEQV. B   Logical
inequivalence (exclusive OR): the expression is true if either A
or B is true, but false if both are true.  .XOR.   A .XOR. B  
Same as .NEQV.  .EQV.  A .EQV. B   Logical equivalence: the
expression is true if both A and B are true, or both are false. 
.NOT.1  .NOT. A   Logical negation: the expression is true if A
is false and false if A is true.  1 .NOT. is a unary operator.
Periods cannot appear consecutively except when the second
operator is .NOT. For example, the following logical expression
is valid:  A+B/(A-1) .AND. .NOT. D+B/(D-1)  Data Types Resulting
from Logical Operation