class_docstr: Class for encoding the CNF expression.
code: def encode_arg(self, arg):
      literal = arg.lit
      value = self.encoding.get(literal, None)
      if value is None:
          n = len(self._symbols)
          self._symbols.append(literal)
          value = self.encoding[literal] = n + 1
      if arg.is_Not:
          return -value
      else:
          return value
  
imports: from itertools import combinations, product, zip_longest
  from sympy.assumptions.assume import AppliedPredicate, Predicate
  from sympy.core.relational import Eq, Ne, Gt, Lt, Ge, Le
  from sympy.core.singleton import S
  from sympy.logic.boolalg import Or, And, Not, Xnor
  from sympy.logic.boolalg import Equivalent, ITE, Implies, Nand, Nor, Xor
label_desc: Use image node_id 8 for calling the EncodedCNF obj's underlying member method code with example usage: obj.encode_arg(arg) and returns: unknown, value