code: def _unary(space,const,name):
      
      if not name in const.vnames:
          return False
      if space.variables[name].discrete:
          values = const.domains[name]
      else:
          values = const.domains[name]
  
      space.domains[name] = space.domains[name].intersection(values)
      return True
docs: Reduce the domain of variable name to be node-consistent with this
      constraint, i.e. remove those values for the variable that are not
      consistent with the constraint.
  
      returns True if the domain of name was modified