in the tutorial, chapter 2., "Relational Data Model Formalities"

(sql490.htm), there is

"set of all k-tuples v1, v2, ... vk, such that v1 [isin] D1, v1 [isin] D1"

i assume it should be
"set of all k-tuples v1, v2, ... vk, such that v1 [isin] D1, v2 [isin] D2"

Divide by Zero

doc/src/sgml/sql.sgml

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  <chapter id="sql">
@@ -235,8 +235,8 @@ D_{1}, v_{2} \in D_{2}, \ldots, v_{k} \in D_{k}$}.
     such that
     <parameter>v<subscript>1</subscript></parameter> &isin; 
     <parameter>D<subscript>1</subscript></parameter>,
-    <parameter>v<subscript>1</subscript></parameter> &isin; 
-    <parameter>D<subscript>1</subscript></parameter>,
+    <parameter>v<subscript>2</subscript></parameter> &isin; 
+    <parameter>D<subscript>2</subscript></parameter>,
     ...
     <parameter>v<subscript>k</subscript></parameter> &isin; 
     <parameter>D<subscript>k</subscript></parameter>.