Olea capensis wood materials. It is also the one of the world's hardest woods according to the Janka hardness test. The timber has a good abrasion resistance and is very strong. It is an excellent turnery wood, and is used for a wide range of decorative items. Olea capensis Olea capensis, also known by the common name black ironwood, is an African tree species belonging to the Olive family (Oleaceae). It is widespread in Sub-Saharan Africa from the east in Somalia, Ethiopia and Sudan, south to the tip of South Africa, and west to Cameroon, Sierra Leone and the Islands of the
NP-hardness nor "Undecidable". For instance, the language of True quantified Boolean formulas is decidable in polynomial space, but not in non-deterministic polynomial time (unless NP = PSPACE). NP-hard problems do not have to be elements of the complexity class NP. As NP plays a central role in computational complexity, it is used as the basis of several classes: NP-hard problems are often tackled with rules-based languages in areas including: NP-hardness NP-hardness (non-deterministic polynomial-time hardness), in computational complexity theory, is the defining property of a class of problems that are, informally, "at least as hard as the hardest problems in NP". A