From AoPSWiki

A dual of a logical statement is a sort of inversion of the statement.

Rigorous definition

Consider a logic statement . For each individual element or operator in , we replace:

• (the universal set) with (the empty set) and vice versa.
• with and vice versa.

Such a statement is the dual of the statement. An interesting fact of logic is that if a logical statement is true, then its dual is true.

See Also

• Logic
• De Morgan's Laws

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