<!DOCTYPE doc [
<!ELEMENT doc (a, b, c, b, c, d) >
<!ELEMENT a EMPTY>
<!ELEMENT b EMPTY>
<!ELEMENT c EMPTY>
<!ELEMENT d EMPTY>
<!ENTITY c "<c/>">
<!ENTITY bc "<b/>&c;">
]>
<doc>
<a/>
&bc;
&bc;
<d/>
</doc>
