code: def most_general_unification(a, b, bindings=None):
      """
      Find the most general unification of the two given expressions
  
      :param a: ``Expression``
      :param b: ``Expression``
      :param bindings: ``BindingDict`` a starting set of bindings with which the
                       unification must be consistent
      :return: a list of bindings
      :raise BindingException: if the Expressions cannot be unified
      """
      if bindings is None:
          bindings = BindingDict()
  
      if a == b:
          return bindings
      elif isinstance(a, IndividualVariableExpression):
          return _mgu_var(a, b, bindings)
      elif isinstance(b, IndividualVariableExpression):
          return _mgu_var(b, a, bindings)
      elif isinstance(a, ApplicationExpression) and isinstance(
          b, ApplicationExpression
      ):
          return most_general_unification(
              a.function, b.function, bindings
          ) + most_general_unification(a.argument, b.argument, bindings)
      raise BindingException((a, b))
  
imports: import operator
  from collections import defaultdict
  from functools import reduce
  from nltk.inference.api import BaseProverCommand, Prover
  from nltk.sem import skolemize
  from nltk.sem.logic import AndExpression, ApplicationExpression, EqualityExpression, Expression, IndividualVariableExpression, NegatedExpression, OrExpression, Variable, VariableExpression, is_indvar, unique_variable
label_desc: Use image node_id 8 for calling a global function with example usage: most_general_unification(a, b, bindings) and returns: bindings, _mgu_var, _mgu_var, unknown