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Explicit Predicate Definitions

p(x₀, ..., x_n-1) : <=> F

• Introduction of new n-ary predicate constant p (definiendum).
• p must not occur within formula F (definiens).
• Free variables of F must be among x₀, ..., x_n-1.
• New axiom

  forall x₀, ..., x_n-1: p(x₀, ..., x_n-1) <=> F

New predicate is uniquely characterized.