What are Tautologies

Tautologies :-

Compound propositions that are always true irrespective of the truth values of the individual simple propositions are called tautologies.

For example, if A1 = 2 | A2 = 3 | A3 = 5
then the compound proposition “Ai is not divisible by 6″ is a tautology.

Some common tautologies defined on universe of discourse X are as follow:

some common tautologies