A proposition does not contain any variable elements. A mathematical proposition is an assembly of symbols and letters formed by following certain rules, with the help of logical connectors. In the calculation of propositions, the propositions used may not have a particular meaning. We can replace a proposition by "Peter is mortal" or "Peter is a man", for example, and what interests the mathematician is the way that the basic propositions are then combined to construct reasoning. The expression "inverse proposition" is the name given to the conditional Q → P in opposition to the proposition P → Q.