Merge pull request #160 from ericprud/master

Clarify that returned `Terms` are novel

Author: elf-pavlik

index.html

@@ -99,6 +99,9 @@ <h2>Design elements and principles</h2>
     <li>Instances of the interfaces created with different libraries should be interoperable.</li>
     <li>Interfaces do <em>not</em> specify how instances are stored in memory.</li>
     <li>Interfaces mandate specific pre-defined methods such as <code>.equals()</code>.</li>
+    <li>
+       Interfaces are not expected to expose internal objects or return the same object from sucessive calls. Callers shoud use the `Term.equals()` function instead of `===` or `==` to test for equivalence. 
+    </li>
     <li>
       Factory functions (e.g., <code>quad()</code>) or methods (e.g.,
       <code>store.createQuad()</code>) create instances.