IFC 4.3.0.1 (IFC4X3) development

# 8.20.3.2 IfcClosedShell

## 8.20.3.2.1 Semantic definition

Informal Propositions:

1. Every edge shall be referenced exactly twice by the loops of the face.
2. Each oriented edge shall be unique.
3. No edge shall be referenced by more than two faces.
4. Distinct faces of the shell do not intersect, but may share edges or vertices.
5. Distinct edges do not intersect but may share vertices.
6. Each face reference shall be unique.
7. The loops of the shell shall not be a mixture of poly loop and other loop types. Note: this is given, since only poly loop is defined as face bound definition.
8. The closed shell shall be an oriented arcwise connected 2-manifold.
9. The Euler equation shall be satisfied. Note: Please refer to ISO 10303-42 for the equation.

## 8.20.3.2.5 Formal representation

ENTITY IfcClosedShell
SUBTYPE OF (IfcConnectedFaceSet);
END_ENTITY;

## 8.20.3.2.6 References

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