Programming, Swift, Object Oriented, Objective C.
computer scientists Barbara Liskov and Jeannette Wing formulated Liskov Substitution Principle: Subtype Requirement: Let ϕ(x) be a property provable about objects x of type T. Then ϕ(y) should be true for objects y of type S where S is a subtype of T. Barbara Liskov and Jeannette Wing Inheritance