diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index bbbffd9d5bb..b9f591296a5 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1055,6 +1055,7 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
        </para>
        <para>
         Factorial
+        (deprecated, use <link linkend="function-factorial"><function>factorial()</function></link> instead)
        </para>
        <para>
         <literal>5 !</literal>
@@ -1068,7 +1069,8 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
         <returnvalue>numeric</returnvalue>
        </para>
        <para>
-        Factorial (as a prefix operator)
+        Factorial as a prefix operator
+        (deprecated, use <link linkend="function-factorial"><function>factorial()</function></link> instead)
        </para>
        <para>
         <literal>!! 5</literal>
@@ -1349,7 +1351,7 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
 
       <row>
        <entry role="func_table_entry"><para role="func_signature">
-        <indexterm>
+        <indexterm id="function-factorial">
          <primary>factorial</primary>
         </indexterm>
         <function>factorial</function> ( <type>bigint</type> )
diff --git a/doc/src/sgml/ref/create_operator.sgml b/doc/src/sgml/ref/create_operator.sgml
index d5c385c087f..66c34e0072f 100644
--- a/doc/src/sgml/ref/create_operator.sgml
+++ b/doc/src/sgml/ref/create_operator.sgml
@@ -87,11 +87,18 @@ CREATE OPERATOR <replaceable>name</replaceable> (
 
   <para>
    At least one of <literal>LEFTARG</literal> and <literal>RIGHTARG</literal> must be defined.  For
-   binary operators, both must be defined. For right  unary
+   binary operators, both must be defined. For right unary
    operators, only <literal>LEFTARG</literal> should be defined, while for left
    unary operators only <literal>RIGHTARG</literal> should be defined.
   </para>
 
+  <note>
+   <para>
+    Right unary, also called postfix, operators are deprecated and will be
+    removed in <productname>PostgreSQL</productname> version 14.
+   </para>
+  </note>
+
   <para>
    The <replaceable class="parameter">function_name</replaceable>
    function must have been previously defined using <command>CREATE
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 2f993ca2e03..0ee303cb87f 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -977,27 +977,8 @@ CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
     Most operators have the same precedence and are left-associative.
     The precedence and associativity of the operators is hard-wired
     into the parser.
-   </para>
-
-   <para>
-    You will
-    sometimes need to add parentheses when using combinations of
-    binary and unary operators.  For instance:
-<programlisting>
-SELECT 5 ! - 6;
-</programlisting>
-   will be parsed as:
-<programlisting>
-SELECT 5 ! (- 6);
-</programlisting>
-    because the parser has no idea &mdash; until it is too late
-    &mdash; that <token>!</token> is defined as a postfix operator,
-    not an infix one.  To get the desired behavior in this case, you
-    must write:
-<programlisting>
-SELECT (5 !) - 6;
-</programlisting>
-    This is the price one pays for extensibility.
+    Add parentheses if you want an expression with multiple operators
+    to be parsed in some other way than what the precedence rules imply.
    </para>
 
    <table id="sql-precedence-table">
diff --git a/doc/src/sgml/typeconv.sgml b/doc/src/sgml/typeconv.sgml
index 8900d0eb383..98662fc91fb 100644
--- a/doc/src/sgml/typeconv.sgml
+++ b/doc/src/sgml/typeconv.sgml
@@ -354,20 +354,19 @@ Some examples follow.
 </para>
 
 <example>
-<title>Factorial Operator Type Resolution</title>
+<title>Square Root Operator Type Resolution</title>
 
 <para>
-There is only one factorial operator (postfix <literal>!</literal>)
+There is only one square root operator (prefix <literal>|/</literal>)
 defined in the standard catalog, and it takes an argument of type
-<type>bigint</type>.
+<type>double precision</type>.
 The scanner assigns an initial type of <type>integer</type> to the argument
 in this query expression:
 <screen>
-SELECT 40 ! AS "40 factorial";
-
-                   40 factorial
---------------------------------------------------
- 815915283247897734345611269596115894272000000000
+SELECT |/ 40 AS "square root of 40";
+ square root of 40
+-------------------
+ 6.324555320336759
 (1 row)
 </screen>
 
@@ -375,7 +374,7 @@ So the parser does a type conversion on the operand and the query
 is equivalent to:
 
 <screen>
-SELECT CAST(40 AS bigint) ! AS "40 factorial";
+SELECT |/ CAST(40 AS double precision) AS "square root of 40";
 </screen>
 </para>
 </example>
diff --git a/src/include/catalog/pg_operator.dat b/src/include/catalog/pg_operator.dat
index 5b0e063655d..4f8b9865eff 100644
--- a/src/include/catalog/pg_operator.dat
+++ b/src/include/catalog/pg_operator.dat
@@ -218,10 +218,10 @@
   oprname => '>=', oprleft => 'xid8', oprright => 'xid8', oprresult => 'bool',
   oprcom => '<=(xid8,xid8)', oprnegate => '<(xid8,xid8)', oprcode => 'xid8ge',
   oprrest => 'scalargesel', oprjoin => 'scalargejoinsel' },
-{ oid => '388', descr => 'factorial',
+{ oid => '388', descr => 'deprecated, use factorial() instead',
   oprname => '!', oprkind => 'r', oprleft => 'int8', oprright => '0',
   oprresult => 'numeric', oprcode => 'numeric_fac' },
-{ oid => '389', descr => 'deprecated, use ! instead',
+{ oid => '389', descr => 'deprecated, use factorial() instead',
   oprname => '!!', oprkind => 'l', oprleft => '0', oprright => 'int8',
   oprresult => 'numeric', oprcode => 'numeric_fac' },
 { oid => '385', descr => 'equal',
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 27989971db7..1dd325e0e6f 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -328,6 +328,7 @@
   proname => 'unknownout', prorettype => 'cstring', proargtypes => 'unknown',
   prosrc => 'unknownout' },
 { oid => '111',
+  descr => 'implementation of deprecated ! and !! factorial operators',
   proname => 'numeric_fac', prorettype => 'numeric', proargtypes => 'int8',
   prosrc => 'numeric_fac' },