Firstly I 'll mention Absorption laws :
- $((\sim p) \vee q) \wedge (\sim q)=(\sim p)$
$((\sim p) \vee q) \wedge p=q$
Also, $p \Longrightarrow q = (\sim p) \vee q$
And, $p \Longleftrightarrow q = (p \Longrightarrow q) \wedge (q \Longrightarrow p)$
Let we have $p \Longrightarrow q = (\sim p) \vee q$
Now, given two absorption laws above, we have $p \Longrightarrow q = [((\sim p) \vee q) \wedge (\sim q)] \vee [(\sim p) \vee q) \wedge p]= [(\sim p) \vee q] \wedge [(\sim q) \vee p]$
So, This expression becomes $p \Longrightarrow q = p \Longleftrightarrow q.$
Where I'm mistaken ?
Correction
Applying Distribution to : $(\lnot p∨q)∧\lnot q$ we get :
In the same way :
Absorption is :