nat ::= 0 | S nat

	dna ::= a | c | t | g | dna dna

	a   c   t    t
	|   |   |    |
	dna dna dna  dna
	|    |  |    |
	  dna   |    |
	  |     |    |
	    dna      |
	     |       |
	        dna

	num ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | num num
	    <= 2^32 - 1

	exp ::= * | + | - | /

	ari ::= num exp num | ari exp ari | ari exp num | num exp ari

	  C ::= [.] exp ari | num exp [.] | num exp num

	  ((4     +   4) /   3  )   *   7
      ((num exp num) exp num) exp num
      [            ] exp num
      [                     ] exp num


      omega = lam x . xx lam x . xx

      lam x . y 
      f(x) = y

      f : x |-> x x 

      f f

      f(f) = f f


	ASSUME RippleAdder  RA+(a, b), RA-(a, b), 

	Convention: a, b, c are nums

		BIG STEP: ->*

	e -> e'   e' -> e''
	--------------------(bigStep)
	e ->* e''


		SMALL STEP: ->


	   e -> e'                            
	--------------(smallStep)          
	C[e] -> C[e']


	RA+(a, b) = c
	--------------(numAdd)
	a + b -> c

	RA*(a, b) = c
	--------------(numMul)
	a * b -> c

	0 != b    RA/(a, b) = c
	------------------------(numDiv)
	a / b -> c

	RA-(a, b) = c
	--------------(numSub)
	a - b -> c



	num.rand := uniform[ 0, 1, ..., largest integer on your computer ]
	exp.rand := unfirom[ *, +, -, / ]
	ari.rand := uniformly choose one of the expression types
	            recurse on its .rands

	(4+5)/(   (2-5)*3)
     ||| |     ||| ||
     ari exp   ari
              |       |