What are the variables used in discrete mathematics proposition calculus?

Propositional variables can represent any proposition.

The meaning of proposition variables in discrete mathematics, the textbook says: Proposition identifiers are used to identify any one of a group of propositions or only indicate the location of any proposition. This is called a proposition variable. For example You live in the dormitory and your bed is 101-1. 101-1 is a proposition identifier and 101 is a set of propositions.

In mathematical logic, in order to express concepts, state theories and rules, it is often necessary to use language to describe. However, the natural language used daily to describe is often not precise enough and is prone to ambiguity. Therefore, it is necessary to introduce a target language. This target language and some formula symbols form a formal symbol system of mathematical logic. The so-called target language is a collection of languages ??that express judgment, and judgment is a form of thinking that affirms or denies something. Therefore, a language or statement that can express judgment is called a proposition.

A proposition always has a "value", which is called truth value. There are only two types of truth values: "true" and "false", which are recorded as true (true) and false (false), represented by symbols t and f respectively. Only declarative sentences with a definite truth value are propositions. All sentences without judgment content, sentences that do not matter right or wrong, such as exclamations, interrogative sentences, imperative sentences, etc. cannot be regarded as propositions. There are two types of propositions: the first type is a proposition that cannot be broken down into simpler statements, which are called atomic propositions; the second type is a proposition that is composed of connectives, punctuation marks and atomic propositions, which is called a compound proposition. All these propositions should have definite truth values.

If a propositional identifier represents a certain proposition, it is called a propositional constant. If a propositional identifier only represents the position mark of any proposition, it is called a propositional variable. Because the propositional variable can represent any proposition, its truth value cannot be determined, so the propositional variable is not a proposition. When the propositional variable p is replaced by a specific proposition, p can determine its truth value. This is also called assigning p. When a propositional argument represents an atomic proposition, the argument is called an atomic argument.