In Boolean algebra (structure), the inclusion relation a\le b is defined as ab'=0 and is the Boolean analogue to the subset relation in set theory. Inclusion is a partial order.
The inclusion relation a can be expressed in many ways:

a

ab'=0

a'+b=1

b'

a+b=b

ab=a
The inclusion relation has a natural interpretation in various Boolean algebras: in the subset algebra, the subset relation; in arithmetic Boolean algebra, divisibility; in the algebra of propositions, material implication; in the twoelement algebra, the set { (0,0), (0,1), (1,1) }.
Some useful properties of the inclusion relation are:
The inclusion relation may be used to define Boolean intervals such that a\le x\le b A Boolean algebra whose carrier set is restricted to the elements in an interval is itself a Boolean algebra.
References

Frank Markham Brown, Boolean Reasoning: The Logic of Boolean Equations, 2nd edition, 2003, p. 52
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