<xs:schema xmlns:tns="http://myns"
targetNamespace="http://myns"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
>
<xs:element name="a" />
<xs:complexType name="c" >
<xs:sequence minOccurs="2" maxOccurs="4">
<xs:sequence minOccurs="19" maxOccurs="20">
<xs:element ref="tns:a" />
</xs:sequence>
</xs:sequence>
</xs:complexType>
<xs:element name="c" type="tns:c" />
</xs:schema>