diff --git a/docs/ref-ch03-query.md b/docs/ref-ch03-query.md
index 74a3e39..9364bcc 100644
--- a/docs/ref-ch03-query.md
+++ b/docs/ref-ch03-query.md
@@ -22,7 +22,8 @@
         | { <qualified-column>
             | <constant> }
             | <scalar-name>
-            | <aggregate-name>( { <column> | <scalar-name> } )
+            | <scalar-query>
+            | <aggregate-function>( { <column> | <scalar-name> } )
           } [ [ AS ] <column-alias> ]
     } [ ,...n ]
   [ ORDER BY [ { <qualified-column> | <column-alias> | <column-ordinal> }
@@ -84,7 +85,12 @@ Set operators `UNION`, etc. apply the previous result set to the next query resu
     | expression <inequality operator> { ALL | ANY} ( <single-column-query> )
     | [ NOT ] EXISTS { <column value> | <single-column-query> } }
 ```
-`DISTINCT FROM` is like equals `=` except comparing two `NOT EXISTS` yields false.
+Since nullable table columns are not allowed, `NOT EXISTS` can only yield `true` on the column of an outer join that is not in a returned row or a `<scalar-query>` that returns nothing. `NULL` is a marker for this case.
+
+`IS [ NOT ] DISTINCT FROM` is a binary operator like [ NOT ] equals `<>`, `=` except comparing two `NOT EXISTS` yields false.
+`A IS DISTINCT FROM B` decodes to: `((A <> B OR A IS NULL OR B IS NULL) AND NOT (A IS NULL AND B IS NULL))`
+`A IS NOT DISTINCT FROM B` decodes to: `(NOT (A <> B OR A IS NULL OR B IS NULL) OR (A IS NULL AND B IS NULL))`
+
 `<single-column-query>` is defined in a CTE and must return only one column.
 
 ```
@@ -98,6 +104,7 @@ Set operators `UNION`, etc. apply the previous result set to the next query resu
     END
   | COALESCE ( <expression> [ ,...n ] )
   | BEGIN <arithmetic on expressions and scalar functions> END
+  | <predicate>
   | *hoon (TBD)
 ```
 If a `CASE` expression uses `<predicate>`, the expected boolean (or loobean) logic applies.
@@ -110,11 +117,16 @@ If it uses `<expression>` `@`0 is treated as false and any other value as true (
   { <column>
     | <scalar-function>
 	  | <scalar-query>
-    | <aggregate-name>( { <column> | <scalar-name> } )
+    | <aggregate-function>( { <column> | <scalar-name> } )
   }
 ```
 `<scalar-query>` is defined in a CTE and must return only one column. The first returned value is accepted and subsequent values ignored.
 
+```
+<aggregate-function> ::=
+  { AVG | MAX | MIN | SUM | COUNT | AND | OR | <user-defined> }
+```
+
 ```
 <column> ::=
   { [ <qualified-column>
diff --git a/urql/lib/parse.hoon b/urql/lib/parse.hoon
index 0a1ce57..73caa5c 100644
--- a/urql/lib/parse.hoon
+++ b/urql/lib/parse.hoon
@@ -561,9 +561,8 @@
   (cold %lt (just '<'))
   (cold %and ;~(plug (jester 'and') whitespace))
   (cold %or ;~(plug (jester 'or') whitespace))
-:: to do %distinct %not-distinct:
-::  (cold %distinct ;~(plug (jester 'is') whitespace (jester 'distinct') whitespace (jester 'from')))
-::  (cold %not-distinct ;~(plug (jester 'is') whitespace (jester 'not') whitespace (jester 'distinct') whitespace (jester 'from')))
+  (cold %distinct ;~(plug (jester 'is') whitespace (jester 'distinct') whitespace (jester 'from') whitespace))
+  (cold %not-distinct ;~(plug (jester 'is') whitespace (jester 'not') whitespace (jester 'distinct') whitespace (jester 'from') whitespace))
     :: ternary operator
   (cold %between ;~(plug (jester 'between') whitespace))
     :: nesting
diff --git a/urql/tests/lib/parse.hoon b/urql/tests/lib/parse.hoon
index 820f04b..0a469c2 100644
--- a/urql/tests/lib/parse.hoon
+++ b/urql/tests/lib/parse.hoon
@@ -1156,9 +1156,21 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
+++  test-predicate-10
+  =/  query  "FROM foo WHERE foobar IS DISTINCT FROM bar SELECT DISTINCT *"
+  =/  pred=(tree predicate-component:ast)  [%distinct foobar bar]
+  %+  expect-eq
+    !>  ~[[%simple-query from-foo [%scalars ~] `pred [%group-by ~] [%having ~] [%select top=~ bottom=~ distinct=%.y columns=~[all-columns]] ~]]
+    !>  (parse:parse(current-database 'db1') query)
+++  test-predicate-11
+  =/  query  "FROM foo WHERE foobar IS NOT DISTINCT FROM bar SELECT *"
+  =/  pred=(tree predicate-component:ast)  [%not-distinct foobar bar]
+  %+  expect-eq
+    !>  ~[[%simple-query from-foo [%scalars ~] `pred [%group-by ~] [%having ~] [%select top=~ bottom=~ distinct=%.n columns=~[all-columns]] ~]]
+    !>  (parse:parse(current-database 'db1') query)
 ::
 ::  remaining simple predicates, varying spacing and keywork casing
-++  test-predicate-10
+++  test-predicate-12
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE foobar  Not  Between foo  And bar ".
     " SELECT *"
@@ -1169,7 +1181,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-11
+++  test-predicate-13
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE foobar  Not  Between foo   bar ".
     " SELECT *"
@@ -1180,7 +1192,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-12
+++  test-predicate-14
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE foobar  Between foo  And bar ".
     " SELECT *"
@@ -1191,7 +1203,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-13
+++  test-predicate-15
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE foobar between foo  And bar ".
     " SELECT *"
@@ -1202,7 +1214,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-14
+++  test-predicate-16
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE T1.foo>=aLl bar ".
     " SELECT *"
@@ -1213,7 +1225,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-15
+++  test-predicate-17
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE T1.foo nOt In bar ".
     " SELECT *"
@@ -1224,7 +1236,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-16
+++  test-predicate-18
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE T1.foo not in (1,2,3) ".
     " SELECT *"
@@ -1235,7 +1247,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-17
+++  test-predicate-19
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE T1.foo in bar ".
     " SELECT *"
@@ -1246,7 +1258,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-18
+++  test-predicate-20
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE T1.foo in (1,2,3) ".
     " SELECT *"
@@ -1257,7 +1269,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-19
+++  test-predicate-21
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE NOT  EXISTS  T1.foo ".
     " SELECT *"
@@ -1268,7 +1280,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-20
+++  test-predicate-22
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE NOT  exists  foo ".
     " SELECT *"
@@ -1279,7 +1291,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-21
+++  test-predicate-23
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE EXISTS T1.foo ".
     " SELECT *"
@@ -1290,7 +1302,7 @@
   %+  expect-eq
     !>  ~[expected]
     !>  (parse:parse(current-database 'db1') query)
-++  test-predicate-22
+++  test-predicate-24
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE EXISTS  foo ".
     " SELECT *"
@@ -1303,7 +1315,7 @@
     !>  (parse:parse(current-database 'db1') query)
 ::
 ::  test conjunctions, varying spacing and keyword casing
-++  test-predicate-23
+++  test-predicate-25
   =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
     " WHERE foobar >=foo And foobar<=bar ".
     " SELECT *"
@@ -1316,7 +1328,7 @@
     !>  (parse:parse(current-database 'db1') query)
 
 :: expected/actual match
-::++  test-predicate-24
+::++  test-predicate-26
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE foobar >=foo And foobar<=bar ".
 ::    " and T1.foo2 = ~zod ".
@@ -1330,7 +1342,7 @@
 ::    !>  (parse:parse(current-database 'db1') query)
 
 :: expected/actual match
-::++  test-predicate-25
+::++  test-predicate-27
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE foobar >=foo And foobar<=bar ".
 ::    " and T1.foo2 = ~zod ".
@@ -1345,7 +1357,7 @@
 ::    !>  (parse:parse(current-database 'db1') query)
 
 :: expected/actual match
-::++  test-predicate-26
+::++  test-predicate-28
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE foobar >=foo And foobar<=bar ".
 ::    " and T1.foo2 = ~zod ".
@@ -1362,7 +1374,7 @@
 ::    !>  (parse:parse(current-database 'db1') query)
 
 :: expected/actual match
-::++  test-predicate-27
+::++  test-predicate-29
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE foobar >=foo And foobar<=bar ".
 ::    " and T1.foo2 = ~zod ".
@@ -1384,7 +1396,7 @@
 ::
 ::  simple nesting
 :: expected/actual match
-::++  test-predicate-28
+::++  test-predicate-30
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE (foobar > foo OR foobar < bar) ".
 ::    " AND T1.foo>foo2 ".
@@ -1402,7 +1414,7 @@
 ::
 ::  nesting
 :: expected/actual match
-::++  test-predicate-29
+::++  test-predicate-31
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE foobar > foo AND foobar < bar ".
 ::    " AND ( T1.foo>foo2 AND T2.bar IN (1,2,3) ".
@@ -1424,7 +1436,7 @@
 ::
 ::  simple nesting, superfluous () around entire predicate
 :: expected/actual match
-::++  test-predicate-30
+::++  test-predicate-32
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE ((foobar > foo OR foobar < bar) ".
 ::    " AND T1.foo>foo2 ".
@@ -1441,7 +1453,7 @@
 
 ::
 ::  aggregate inequality
-++  test-predicate-31
+++  test-predicate-33
   =/  select  "from foo where  count( foobar )  > 10 select * "
   =/  pred=(tree predicate-component:ast)  [%gt [aggregate-count-foobar ~ ~] literal-10]
   %+  expect-eq
@@ -1449,7 +1461,7 @@
     !>  (parse:parse(current-database 'db1') select)
 ::
 ::  aggregate inequality, no whitespace
-++  test-predicate-32
+++  test-predicate-34
   =/  select  "from foo where count(foobar) > 10 select *"
   =/  pred=(tree predicate-component:ast)  [%gt [aggregate-count-foobar ~ ~] literal-10]
   %+  expect-eq
@@ -1457,7 +1469,7 @@
     !>  (parse:parse(current-database 'db1') select)
 ::
 ::  aggregate equality
-++  test-predicate-33
+++  test-predicate-35
   =/  select  "from foo where bar = count(foobar) select *"
   =/  pred=(tree predicate-component:ast)  [%eq bar [aggregate-count-foobar ~ ~]]
   %+  expect-eq
@@ -1466,7 +1478,7 @@
 ::
 ::  complext predicate, bug test
 :: expected/actual match
-::++  test-predicate-34
+::++  test-predicate-36
 ::  =/  query  "FROM adoptions AS T1 JOIN adoptions AS T2 ON T1.foo = T2.bar ".
 ::    " WHERE  A1.adoption-email = A2.adoption-email  ".
 ::    "  AND     A1.adoption-date = A2.adoption-date  ".