In a previous question about [exotic state machines][1], Alex ten Brink and Raphael addressed the computational capabilities of a peculiar kind of state machine: min-heap automata. They were able to show that the set of languages accepted by such machines ($HAL$) is neither a subset nor a superset of the set of context-free languages. Given the successful resolution of and apparent interest in that question, I proceed to ask several follow-up questions.

It is known that the regular languages are closed under a variety of operations (we may limit ourselves to basic operations such as union, intersection, complement, difference, concatenation, Kleene star, and reversal), whereas the context-free languages have different closure properties (these are closed under union, concatenation, Kleene star, and reversal).
> Is HAL closed under reversal?

  [1]: http://cs.stackexchange.com/q/110/69