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Well-formed formulas (wffs)

Well-formed formula, often shortened to wffs, are true or
false statements. For example, (< (3) (7)) is a well-formed formula and
so is (= (6) (4). Ghilbert uses Greek symbols for wffs like φ, ψ, χ, τ, and θ. Relationships between well-
formed formulas are the subject of Propositional logic.

Propositional Logic