(DrRacket should really do that.) original commit: 40124a0619da5e187d95aeb1dde237f05d6f9c6b
and documented and adjusted these libraries: racket/contract/base racket/contract/exists racket/contract/parametric (renamed from exists) racket/contract/region original commit: 21cbd9ad81eb35dc4d39d6063db25fcb1cc94bbc
original commit: 8afeed8c663242159ac08ac043ccf860779ddd91
original commit: 10eb818f953a4160b7f3c91193739f1451bf192c