One means of demonstrating that a given problem \(X\) is \(\textbf{NP}\)-hard is to show that \(\sc{BHP}\) may be reduced to it. But since most mathematically natural problems bear no relationship to Turing machines, it is by no means obvious that such reductions exist. This problem was circumvented at the beginning of the study of \(\textbf{NP}\)-completeness by Cook (1971) and Levin (1973) who independently demonstrated the following:[17]