1. The Design of APL
2. {4} The American Heritage Dictionary of the English Language Houghton Mifflin Company. {4} The American Heritage Dictionary of the English Language Houghton Mifflin Company.
3. {5} Berry P. C. SHARP APL Pocket Reference Toronto I. P. Sharp Associates 1984. Publication 0199 8409 E3 R1. {5} Berry P. C. SHARP APL Pocket Reference Toronto I. P. Sharp Associates 1984. Publication 0199 8409 E3 R1.