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2.2.1 The Interface Component

An interface can optionally extend one or more other interfaces. To avoid circular definitions, an interface MUST NOT appear as an element of the set of interfaces it extends, either directly or indirectly. The set of operations available in an interface includes all the operations defined by the interfaces it extends directly or indirectly, together with any operations it directly defines. The operations directly defined on an interface are referred to as the declared operations of the 
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"element" in the second sentence is ambiguous wrt XML element.

Proposed resolution: "appear as an element of the set" => "appear in the set".