code: def in_constraint(self, node1, node2):
          
          constraint = constraint_table[node2]
          if constraint == 0b0:
              return False
  
          try:
              value = self.el2bv[node1]
          except KeyError:
              return False
  
          return constraint & value != 0
docs: Checks if node1 is in node2's constraints
          For instance, if node1 = 010 and node2 = 110:
          010 & 110 = 010 -> has the element.