The Wolfram Language has a flexible system for specifying arbitrary symbolic assumptions about variables. It uses a wide range of sophisticated algorithms to infer the consequences of assumptions—often in the process automatically proving a sequence of necessary mathematical theorems.
Element (∈) — specify membership in a domain (entered as elem)
NotElement (∉) — specify exclusion from a domain (!elem)
Less (<), Greater (>), ...— define inequalities, implicitly for real numbers