1. Consider procedure calls that may be taken to be instances of the USES relation. Mutually recursive modules do not form a hierarchy. Direct recursion within a module, however, is allowed in a hierarchy. Are these statements correct? If so, what is their justification? 2. Can you define the concept of level for a general graph rather than for a DAG? Why? Why not? What does this imply about a USES relation that is not a hierarchy?