## 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.