code: def find_unit_clause(clauses, model):
      """
      A unit clause has only 1 variable that is not bound in the model.
  
      >>> from sympy.abc import A, B, D
      >>> from sympy.logic.algorithms.dpll import find_unit_clause
      >>> find_unit_clause([A | B | D, B | ~D, A | ~B], {A:True})
      (B, False)
  
      """
      for clause in clauses:
          num_not_in_model = 0
          for literal in disjuncts(clause):
              sym = literal_symbol(literal)
              if sym not in model:
                  num_not_in_model += 1
                  P, value = sym, not isinstance(literal, Not)
          if num_not_in_model == 1:
              return P, value
      return None, None
  
file_path: sympy/sympy/logic/algorithms/dpll.py
imports: from sympy.core.sorting import default_sort_key
  from sympy.logic.boolalg import Or, Not, conjuncts, disjuncts, to_cnf, to_int_repr, _find_predicates
  from sympy.assumptions.cnf import CNF
  from sympy.logic.inference import pl_true, literal_symbol
label_desc: Use image node_id 9 for calling a global function with example usage: find_unit_clause(clauses, model) and returns: None,  None, P,  value