Mark has been assigned to research a case for the firm's client, Desiree Darden, which relates to a contract for the sale of goods in Illinois on credit. Mark asks you for advice about legal research. He has located several legal resources, and all of them seem to address facts and issues that are similar to the facts in the Darden case. He is not sure how to get started in evaluating which sources are most useful for the case. You decide to write him an e-mail in which you discuss some basic legal concepts that will help him with starting research, and help him evaluate which sources will be most relevant to his research of the Darden case. Mark located the following sources:

Illinois Uniform Commercial Code Act (applies to the sale of goods)
Wisconsin Uniform Commercial Code Act
U.S. Code (federal statute) - Consumer Credit Act
Cost v. Stern - a decision of the supreme court of Michigan
Smith v. Jones - a decision of the intermediate appeals court in Illinois
Garrity v. Acme. - a decision of the supreme court in Illinois
Standard v. Poors - a federal supreme court case involving the federal Consumer Credit Act
An American Jurisprudence entry that addresses the type of situation of your law firm's client
Restatements of the Law entry covering sales and consumer credit

In your e-mail, you should address the following issues:

a) What are the main sources of U.S. law?

b) In case law, what is meant by precedent and stare decisis?

c) What is the difference between primary authority and secondary authority? Which of the sources that Mark located are primary and which are secondary?

d) What is the difference between mandatory (binding authority) and persuasive authority? Which of the sources that Mark located could be mandatory authority for the Darden case?

e) Explain which sources that Mark found would have the most value as precedent and authority for the Darden case; being sure to explain why.