diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index e6923c3..c27d743 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -51,125 +51,127 @@
The usual logical operators are available:
+
-
- AND (operator)
-
-
-
- OR (operator)
-
+
+ AND (operator)
+
-
- NOT (operator)
-
+
+ OR (operator)
+
-
- conjunction
-
+
+ NOT (operator)
+
-
- disjunction
-
+
+ conjunction
+
-
- negation
-
+
+ disjunction
+
-
- AND
- OR
- NOT
-
+
+ negation
+
+
+ AND
+ OR
+ NOT
+
+
+
SQL uses a three-valued Boolean logic where the null value represents
unknown
. Observe the following truth tables:
+
-
-
-
-
- a
- b
- a AND b
- a OR b
-
-
+
+
+
+
+ a
+ b
+ a AND b
+ a OR b
+
+
-
-
- TRUE
- TRUE
- TRUE
- TRUE
-
+
+
+ TRUE
+ TRUE
+ TRUE
+ TRUE
+
-
- TRUE
- FALSE
- FALSE
- TRUE
-
+
+ TRUE
+ FALSE
+ FALSE
+ TRUE
+
-
- TRUE
- NULL
- NULL
- TRUE
-
+
+ TRUE
+ NULL
+ NULL
+ TRUE
+
-
- FALSE
- FALSE
- FALSE
- FALSE
-
+
+ FALSE
+ FALSE
+ FALSE
+ FALSE
+
-
- FALSE
- NULL
- FALSE
- NULL
-
+
+ FALSE
+ NULL
+ FALSE
+ NULL
+
-
- NULL
- NULL
- NULL
- NULL
-
-
-
-
+
+ NULL
+ NULL
+ NULL
+ NULL
+
+
+
+
-
-
-
-
- a
- NOT a
-
-
+
+
+
+
+ a
+ NOT a
+
+
-
-
- TRUE
- FALSE
-
+
+
+ TRUE
+ FALSE
+
-
- FALSE
- TRUE
-
+
+ FALSE
+ TRUE
+
-
- NULL
- NULL
-
-
-
-
-
+
+ NULL
+ NULL
+
+
+
+
The operators AND and OR are