sketchpad
     
        a program that allowed users to draw on a screen with a light
        pen.  it supported constraints e.g. drawing a constrained
        ellipse produced a circle.  it also had some computer aided
        design features e.g. computing loads on beams.
     
        sketchpad was the subject of ivan e. sutherland's 1963 mit
        phd thesis, which opened the field of computer graphics.  it
        was the progenitor of computer drawing packages like macdraw
        or adobe illustrator.  there is a film of sketchpad in
        action.
     
        it solved constraints using value inference and introduced
        the "ring" list structure.
     
        "sketchpad: a man-machine graphical communication system",
        i.e. sutherland, mit lincoln lab, tr 296 jan 1963.
     
        sammet 1969, p. 678.
     
        1995-02-14
     
     
see also:
light pen computer aided design ivan e. sutherland mit computer graphics macdraw 
adobe illustrator constraint value inference ring