The significance of propositional variables in discrete mathematics, the textbook says: Propositional identifiers are used to identify any one of a group of propositions or only to indicate the position of any one proposition, which is called propositional variables at this time. For example, if you live in a dormitory and your bed is 10 1- 1, then 10 1 is a proposition identifier.

In mathematical logic, in order to express concepts and state theories and rules, it is often necessary to use language to describe them, but the natural language used in daily life is often inaccurate and unclear, so it is necessary to introduce a target language. This target language and some formula symbols constitute the formal symbol system of mathematical logic. The so-called target language is a collection of languages that express judgment. Judgment is a form of thinking that affirms or denies things, so it can express judgment. This is called a proposition.

A proposition always has a "value", which is called the truth value. There are only two kinds of truth values: "true" and "false", which are recorded as true and false respectively, and are represented by symbols T and F respectively. Only declarative sentences with certain truth values are propositions, and all sentences that do not judge the content, exclamatory sentences, interrogative sentences, imperative sentences and other sentences that do not distinguish right from wrong cannot be regarded as propositions. There are two kinds of propositions: the first kind cannot be decomposed into simpler sentences, which are called atomic propositions; The second is a proposition composed of conjunctions, punctuation marks and atomic propositions, which is called a compound proposition. All these propositions should have definite truth values.

If a proposition identifier represents a definite proposition, it is called a proposition constant, and if it only represents the position symbol of any proposition, it is called a proposition argument. Propositional argument is not a proposition because it can represent any proposition and its true value cannot be determined. When the propositional argument P is replaced by a concrete proposition, the true value of P can be determined, which is also called assignment P. When a propositional argument represents an atomic proposition, it is called atomic argument.