Document contains a chapter at position.
PermanentFact = False
HiddenFact = False
InternalUniquenessConstraint15
InternalUniquenessConstraint
It is possible that some document contains a chapter at more than one position
and that for some position, more than one document contains a chapter at that position.
In each population of document contains a chapter at position, each document, position combination occurs at most once.
This association with document, position provides the preferred identification scheme for document component.