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The diagramming notation described in this document can also be used to describe the relationship between two different SNOMED CT expressions.

This is represented by two expression diagrams, one above the other, separated by a relational operator between. The diagram is read top to bottom.

Figure 9 Expression relation diagram

As an example below is a diagram showing two expressions that are equivalent:

Figure 10 Diagram showing equivalence of two expressions

Note that in this example the equivalence relation connects the two expressions with lines – indicating that the relationship is bidirectional and can be read either way.

Figure 11 shows an expression (top) subsumed by another expression (bottom). Note that arrows have been used to connect the expressions to the relational operator to indicate the direction it must be read.

Figure 12 shows an expression (top) that subsumes an expression (bottom). Again note arrows have been used to indicate the direction this relationship must be read.

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