anchor.diff:    (let ((tab (make-array (list linhas colunas)))
   	(i 0))
       (dolist (v (psr-variaveis-todas p) tab)
  -      (setf (aref tab (floor i colunas) (mod i colunas)) (first (gethash v (psr-pares p))))
  +      (setf (aref tab (floor i colunas) (mod i colunas)) (first (elt (gethash v (psr-pares p)) 0)))
         (incf i))))
   
   ;;;; 2.2.2
  
positive.code: (defun cria-psr (variaveis dominios restricoes)
    ""
    (let ((pares (make-hash-table :test 'equal)))
      (mapcar #'(lambda (v d) (setf (gethash v pares) d)) variaveis dominios)
      (make-psr :variaveis-todas variaveis :pares pares :restricoes restricoes)))
  
  
  
negative.code: (defun psr-atribuicoes (p)
    "Retorna uma lista com todas as atribuicoes - pares (variavel . valor) - do PSR."
    (let ((atribuicoes (list)))
      (maphash #'(lambda (v dr) (when (= (length (elt dr 0)) 1)
  				(push (cons v (first (elt dr 0))) atribuicoes))) 
  	     (psr-pares p))
      atribuicoes))
  
  