In Exercises 3-6, name the property that the statement illustrates.
3. If P Q≅S T and S T≅U V then P Q≅U V
4. ∠F ≅∠F
5. If X Y≅U V, then ≅U V≅X Y
6. If ∠L ≅∠M and ∠M ≅∠N then ∠L ≅∠ N.