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 4. Find an article or a book chapter on the philosophy or principles of UNIX operating systems. Discuss two particular principles and explain their connections to programming languages. 5. Find a paper or a book on structured programming. Briefly describe the main ideas of structured programming. (Provide complete reference information of the paper or book.) 6. Read the paper: Donald E. Knuth, Literate Programming. Give a brief summary of "Literate Programming."