The following story is from N. Wirth’s (1976) Algorithms + data structures = programs. I married a widow (let’s call her W) who has a grown-up daughter (call her D). My father (F), who visited us quite often, fell in love with my stepdaughter and married her. Hence my father became my son-in-law, and my stepdaughter became my mother. Some months later, my wife gave birth to a son (S₁), who became the brother-in-law of my father, as well as my uncle. The wife of my father, that is, my stepdaughter, also had a son (S₂). Using predicate calculus, create a set of expressions that represent the situation in the above story. Add expressions defining basic family relationships such as the definition of father-in-law and use modus ponens on this system to prove the conclusion that “I am my own grandfather.”