Vanderbeek, Greg (June 2007). Order of Operations and RPN (Expository paper). Master of Arts in Teaching (MAT) Exam Expository Papers. Lincoln, Nebraska, USA: University of Nebraska. Paper 46. Diarkibkan daripada yang asal pada 2020-06-14. Dicapai pada 2020-06-14.
Vanderbeek, Greg (June 2007). Order of Operations and RPN (Expository paper). Master of Arts in Teaching (MAT) Exam Expository Papers. Lincoln, Nebraska, USA: University of Nebraska. Paper 46. Diarkibkan daripada yang asal pada 2020-06-14. Dicapai pada 2020-06-14.