code: public Expression2 getUnevaluatedLogicalForm(Environment env, IndexedList<String> symbolTable) {
      List<String> newBindings = Lists.newArrayList();
      return getUnevaluatedLogicalForm(env, symbolTable, newBindings);
    }
docs: Gets an expression that evaluates to the denotation of
  this parse. The expression will not re-evaluate any
  already evaluated subexpressions of this parse. {@code env}
  may be extended with additional variable bindings to
  capture denotations of already-evaluated subparses.
  
  @param env
  @param symbolTable
  @return