We study the expressive power of Alternating Parity Krivine Automata (APKA). which provide operational semantics to Higher-Order Modal Fixpoint Logic (HFL). APKA consist of ordinary parity automata extended by a variation of the Krivine Abstract Machine. We show that the number and parity of priorities available to an APKA form a proper hierarchy of expressive power as in the modal mu... https://www.fitnessgravesyardes.shop/product-category/thumb-control/