Exercise 4.11 - tweaking the data representation of frames, apparently just for kicks
unmodified code from text
lookup and set! differ in only ONE LINE, and this really popped out at me while i was reading...
Exercise 4.12 - refactored the (perhaps embarrassingly) unDRY code in 4.1.3
notes on sol
Exercise 4.13 - unbinding a variable from ALL environments. if it had been named 'undefine', i would've stopped at the current frame
oh they want the whole thing implemented as a special form. ok then...