Onager a subspecies of the onager as "E. hemionus kiang", but recent molecular studies indicate it to be a distinct species, having diverged from the closest relative of the Mongolian wild ass's ancestor less than 500,000 years ago. Widely five recognized subspecies of the onager include: A sixth possible subspecies, the Gobi khulan ("E. h. luteus", also called the "chigetai" or "dziggetai") has been proposed, but may be synonymous with "E. h. hemionus". Debates over the taxonomic identity of the onager occurred until 1980. As of today, four living subspecies and one extinct subspecies of the Asiatic wild ass have been
Type system or an "effect system", which enables even more program specifications to be verified by a type checker. Beyond simple value-type pairs, a virtual "region" of code is associated with an "effect" component describing "what" is being done "with what", and enabling for example to "throw" an error report. Thus the symbolic system may be a "type and effect system", which endows it with more safety checking than type checking alone. Whether automated by the compiler or specified by a programmer, a type system makes program behavior illegal if outside the type-system rules. Advantages provided by programmer-specified type systems include: Advantages