(define nand-gate
  {number --> number --> number}
   1 1 -> 0
   1 0 -> 1
   0 1 -> 1
   0 0 -> 1)
   
(define nand-gate
  {number --> number --> number}
   1 1 -> 0
   X Y -> 1)  
   
(define nand-gate
  {number --> number --> number}
   1 1 -> 0
   _ _ -> 1) 
   
(define invert
  {number --> number}
   X -> (nand-gate X X))
   
(define and-gate
  {number --> number --> number}
   X Y -> (invert (nand-gate X Y)))
   
(define or-gate
  {number --> number --> number}
   X Y -> (nand-gate (invert X) (invert Y)))
   
(define nor-gate
  {number --> number --> number}
   0 0 -> 1
   _ _ -> 0)
   
(define invert
  {number --> number}
   X -> (nor-gate X X))
   
(define or-gate
  {number --> number --> number}
   X Y -> (invert (nor-gate X Y)))         
  
(define and-gate
  {number --> number --> number}
   X Y -> (nor-gate (invert X) (invert Y)))