public <TCollection, TResult> Queryable<TResult> selectMany(
     FunctionExpression<Function2<T, Integer, Enumerable<TCollection>>> collectionSelector,
     FunctionExpression<Function2<T, TCollection, TResult>> resultSelector) {
   return factory.selectMany(getThis(), collectionSelector, resultSelector);
 }
 public <TResult> Queryable<TResult> selectMany(
     FunctionExpression<Function1<T, Enumerable<TResult>>> selector) {
   return factory.selectMany(getThis(), selector);
 }