code: def precondition_approximate_contraction(
      state, op, model, guide, approx_vars
  ):
      # Eagerly winnow approx_vars.
      approx_vars = approx_vars.intersection(guide.input_vars)
      if not approx_vars:
          return model
  
      terms = [
          term
          for term in guide.terms
          if not approx_vars.isdisjoint(term.input_vars)
      ]
      if len(terms) == 1:
          guide = terms[0]
          return Approximate(ops.logaddexp, model, guide, approx_vars)
      raise NotImplementedError("TODO")
  
file_path: funsor/funsor/precondition.py
imports: from collections import OrderedDict
  from .None import ops
  from .cnf import Contraction, GaussianMixture
  from .domains import Reals
  from .gaussian import Gaussian
  from .interpretations import StatefulInterpretation
  from .terms import Approximate, Funsor, Subs, Variable
label_desc: Use image node_id 2 for calling a global function with example usage: precondition_approximate_contraction(state, op, model, guide, approx_vars) and returns: model, Approximate