 different functions. In first-semester calculus,
  after reviewing functions, you learned how to compute limits of
  functions, and then used those ideas to develop the derivative of
  a function. The exact same process is used to develop calculus in
  high dimensions. One glitch that will prevent us from developing
  calculus this way in high dimensions is the epsilon-delta
  definition of a limit. We'll review it briefly. Those of you who
  want to pursue further mathematical study will spend much more
 