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: b8c7a753d3e6c06190cbe3560610710c48131960
original commit: 939af28a4c94c283f46eb121574e4131f12cba53
original commit: 28b404307793f041bb3363135a2968e283855318