The classes \(\textbf{NP}\) (non-deterministic polynomial time), \(\textbf{NPSPACE}\) (non-deterministic polynomial space), \(\textbf{NEXP}\) (non-deterministic exponential time), and \(\textbf{NL}\) (non-deterministic logarithmic space) are defined analogously to \(\textbf{P}\), \(\textbf{NP}\), \(\textbf{EXP}\) and \(\textbf{L}\) – e.g. \(\textbf{NP} = \bigcup_{k \in \mathbb{N}} \textbf{NTIME}(n^k)\).