329 ;;Quote: Sketchpad allows man and computer to converse rapidly through line drawings; typing only needed for legends

331 ;;Quote: Sketchpad maintains constraints for vertical lines, parallel/perpendicular lines, points on circle, upright symbols, equal size symbols; specialized constraints as needed

331 ;;Quote: Sketchpad stores how a drawing is tied together; a hexagon stays closed despite being moved

331+;;Quote: Sketchpad stores the structure of subpictures

332 ;;Quote: worth drawing a circuit in Sketchpad if could also simulate the circuit

332 ;;Quote: besides Ross's n-component elements, Sketchpad includes back-pointers stored in a ring; e.g., e.g., ring of line segments that terminate on a point

332 ;;Quote: ring operations to insert, remove, copy, foreach forward/backward; no special cases for empty and one member rings

333 ;;Quote: Sketchpad can perform basic operations on any drawing part (e.g., display); allows changing the specific details without changing the general parts

333 ;;Quote: a Sketchpad type is a ring of objects under a generic heading; the generic heading defines the type and its subroutines

333+;;Quote: constructing a new type in Sketchpad is a finite, well-defined task; construct a generic block of 20 registers and the corresponding subroutines

333 ;;Quote: Sketchpad is organized into a Universe of Variables, Holders, Constraints, and Types; the later includes Lines, Circles, and Pictures

334 ;;Quote: loss of tracking is the termination signal for Sketchpad; finish a drawing with a quick flick of the pen; the tracking program fails

334 ;;Quote: Sketchpad tracks the pseudo pen location, a bright dot at the nearest drawing part; used for drawing operations

334 ;;Quote: Sketchpad supports most straight edge and compass constructions; topological relationships via pseudo pen location and demonstrative language

334 ;;Quote: Sketchpad uses a Tx-2 scope that displays upto 100,000 spots/second on a 1024x1024 grid

335 ;;Quote: 36-bits per spot for display location and an n-component element; e.g., the spots for a subpicture point to that subpicture's ring

336 ;;Quote: use toggle switches to display Sketchpad's abstractions; e.g., constraint is a circle and code letter with four arms to the constrained variables

336 ;;Quote: Sketchpad includes general functions that are independent of type; e.g., expand an instance of a subpicture; powerful

337 ;;Quote: Sketchpad provides general functions for expansion of instances, recursive deletion, and recursive merging of subpictures

337 ;;Quote: when merge objects of the same type, a single object results with dependencies updated recursively; e.g., merging lines merges their endpoints

340 ;;Quote: a constraint is a subroutine yielding a scalar that should be zero; use one pass method or relaxation; e.g., can analyze force distribution of a pin connected truss

341 ;;Quote: one pass method for constraint satisfaction; recursively locate free variables that are easily satisfied; re-evaluate in reverse order

343 ;;Quote: use Sketchpad to animate a face or pedal a bike