code: def propdemo(trace=None):
      """Example of a propositional model."""
  
      global val1, dom1, m1, g1
      val1 = Valuation([("P", True), ("Q", True), ("R", False)])
      dom1 = set()
      m1 = Model(dom1, val1)
      g1 = Assignment(dom1)
  
      print()
      print("*" * mult)
      print("Propositional Formulas Demo")
      print("*" * mult)
      print("(Propositional constants treated as nullary predicates)")
      print()
      print("Model m1:\n", m1)
      print("*" * mult)
      sentences = [
          "(P & Q)",
          "(P & R)",
          "- P",
          "- R",
          "- - P",
          "- (P & R)",
          "(P | R)",
          "(R | P)",
          "(R | R)",
          "(- P | R)",
          "(P | - P)",
          "(P -> Q)",
          "(P -> R)",
          "(R -> P)",
          "(P <-> P)",
          "(R <-> R)",
          "(P <-> R)",
      ]
  
      for sent in sentences:
          if trace:
              print()
              m1.evaluate(sent, g1, trace)
          else:
              print(
                  f"The value of '{sent}' is: {m1.evaluate(sent, g1)}"
              )
  
imports: import inspect
  import re
  import sys
  import textwrap
  from pprint import pformat
  from nltk.decorators import decorator
  from nltk.sem.logic import AbstractVariableExpression, AllExpression, AndExpression, ApplicationExpression, EqualityExpression, ExistsExpression, Expression, IffExpression, ImpExpression, IndividualVariableExpression, IotaExpression, LambdaExpression, NegatedExpression, OrExpression, Variable, is_indvar
label_desc: Use image node_id 7 for calling a global function with example usage: propdemo(trace) without return types