
Main Concept :
Tautology in mathematical reasoning
Tautology: A statement pattern is called a tautology, if it is always true, whatever may be the truth values of constitute statements.
A tautology is called a theorem or a logically valid statement pattern. A tautology is always true for all possible truth values of its component statements.
Other Concepts :
Concept 1 :
Negation of a statement in mathematical reasoning
The denial of a statement p is called its negation, written as ~ p. Negation of any statement p is formed by writing "It is not the case that ..... "or " It is false that......." before p or, if possible by inserting in p the word "not".
Negation is called a connective although it does not combine two or more statements. In fact, it only modifies a statement.
Negation of compound statements:
We have learnt about negation of a simple statement. Writing the negation of compound statements having conjunction, disjunctions, implication, equivalence, etc, is not very simple. So, let us discuss the negation of compound statement.

Concept 2 :
Simple & Compound statements in mathematical reasoning
(i) Simple statements: Any statement or proposition whose truth value does not explicity depend on another statement is said to be a simple statement.
In other words, a statement is said to be simple if it cannot be broken down into simpler statements, that is, if it is not composed of simpler statements.
(ii) Compound statements: If a statement is combination of two or more simple statements, then it is said to be a compound statement or a compound proposition