The let Construction:

    - See DEMO.  The function repeat_square_1 takes roughly 2^i steps
      (as opposed to i) since it computes the same thing twice on each
      iteration.  

    - The let construction allows you to store a value in a particular
      variable for the use in another calculation.  The syntax is 

      (let ( (name_1 value_1)
		    .
		    .
		    .
	     (name_n value_n)
	   )

	   (expression using name_i)
      )

      where the name_i are locally assigned the value_i for use in the
      expression. 

      See DEMO for the let construction used in the repeat_square
      example.

    - If you want to use name_i in value_k for k > i, then use 'let*'
      instead of 'let'.  'let*' is equivalent to nested 'let's, i.e.

      (let ( (name_1 value_1) ) (let ( (name_2 (f(name_1))) ) (...) ) 

      is equivalent to 

      (let* ( (name_1 value_1) (name_2 f(value_2)) ) (...) )

      See the DEMO for an illustration of this.


Parsing:

    - See Assignment 3 for information


Local Definitions:

    - Local definitions are function definitions within functions
      (e.g. parse_formula on Asst 3).  They are useful for
      organizational purposes, typically when a function is only
      relevant for use within another.