An n-instruction Turing machine is a Turing machine having an arbitrary number of states and symbols, but having only n defined transitions/instructions in its transition table (all others are undefined).| wiki.bbchallenge.org
The 2-state, 5-symbol Busy Beaver problem, BB(2,5), is unsolved. With the discovery of the Cryptid machine Hydra in April 2024, we now know that we must solve a Collatz-like problem in order to solve BB(2,5) and thus BB(2,5) is Hard.| wiki.bbchallenge.org
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Lovecraftian Beaver fan art made by LaurenCryptids are Turing Machines whose behavior (when started on a blank tape) can be described completely by a relatively simple mathematical rule, but where that rule falls into a class of unsolved (and presumed hard) mathematical problems. This definition is somewhat subjective (What counts as a simple rule? What counts as a hard problem?). In practice, most currently known small Cryptids have Collatz-like behavior. In other words, the halting problem ...| wiki.bbchallenge.org