A relation R on a set A is a **partial order** if it is reflexive, anti-symmetric, and transitive. The notation a ≼ b is used to express aRb, reflecting the fact that a *partial order* acts like the ≤ operator on the elements of A.

The expression a ≼ b is read “a is at most b.”

The difference between the ≼ and the ≤ symbols is the slight curve in the ≼ symbol. The domain, along with a partial order defined on it, is denoted (A, ≼) and is called a “partially ordered set” or “**poset**.”

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