##### Basics of Propositional Logic-2

For a conditional statement p→q, we can write three related conditional statements as,

**Converse**: q → p

**Contrapositive**: ¬q → ¬p

**Inverse**: ¬p → ¬q

*Only Contrapositive will have same truth values as p→q.*

**Tautology**:- A compound statement which is **always true** is called a *tautology*.

**Contradiction**:- A compound statement which is **always false** is called a *contradiction*.

**Contingency**:- A compound statement which is **neither a tautology nor a contradiction** is called a *contingency*.

**Logically equivalent:- **The compound propostions p and q are called logically equivalent** if p↔q is a tautology.
Satisfiability:-**A formula is called

*satisfiable*if it is true for atleast one case or interpretation.

**Validity:-**A formula is called

*valid*if it is true in all the cases or interpretation.