&gt; You cannot use formal equivalence to prove practical ease of doing the problem.<p>Agree completely, but want to bring it back to another computing topic: Technically, anything that can be computed with one Turing-complete language can be computed with another. And every language <i>clearly</i> is not equivalent in terms of ease of understanding and reasoning about as every other language.<p>Trivially, compare computations in brainfuck to computations in C. Compare the recursive definition of tree traversal available in lisps to languages without recursion (some BASIC variants and others) where you have to jump through hoops and self-manage a stack.