http://download.library1.org/main/1309000/90db32d070cfb70ca617e655d5c35529/Alfred%20V.%20Aho%2C%20Monica%20S.%20Lam%2C%20Ravi%20Sethi%2C%20Jeffrey%20D.%20Ullman%20-%20Compilers%20-%20Principles%2C%20Techniques%2C%20and%20Tools-Pearson_Addison%20Wesley%20%282006%29.pdf