code: def expr_contains(e, o):
      ''' Returns true if o is in e '''
      if o == e:
          return True
      if e.has_args():
          for a in e.args():
              if expr_contains(a, o):
                  return True
      return Falsf expr_contains(e, o):
      ''' Returns true if o is in e '''
      if o == e:
          return True
      if e.has_args():
          for a in e.args():
              if expr_contains(a, o):
                  return True
      return False
docs: Returns true if o is in e