In judicial opinions, the use of "defeasible" is commonplace. There is however disagreement among legal logicians whether "defeasible reasoning" is central, e.g., in the consideration of "open texture", precedent, , and "rationales", or whether it applies only to explicit defeasance clauses. H.L.A. Hart in "The Concept of Law" gives two famous examples of defeasibility: "No vehicles in the park" (except during parades); and "Offer, acceptance, and memorandum produce a contract" (except when the contract is illegal, the parties are minors, inebriated, or incapacitated, etc.).