Chapters: 1: Introduction 2: Simple example 3: Invocation 4: Finer Control 5: X-Y Plots 6: Contour Plots 7: Image Plots 8: Examples 9: Gri Commands 10: Programming 11: Environment 12: Emacs Mode 13: History 14: Installation 15: Gri Bugs 16: Test Suite 17: Gri in Press 18: Acknowledgments 19: License Indices: Concepts Commands Variables | ### 10.9.3: Tertiary Rpn Operators `{rpn 0 4 "hello" substr }` Extract 4 characters from the indicated string, starting at character number 0 (i.e. the start of the string). In other words, replace the three items on the top of the stack with the single item ``\"hell\"`'.