Finding the principal disjunctive normal form (PDNF) of a Boolean expression Find the principal disjunctive normal form (PDNF) of a Boolean expression 
$$((p\wedge q) \rightarrow r)\vee((p\wedge q)\rightarrow \neg r).$$
I  tried by expanding it but I am stuck with the expression 
$(\neg p \vee \neg q \vee r) \vee (\neg p \vee \neg q \vee \neg r)$. I don't know how to convert them into min terms. Please help me.
Expression mentioned is a Tautology.
$$((p.q) \rightarrow r)+((p.q)\rightarrow r')=((p'+q'+r)+(p'+q'+r'))=p'+q'+1 = 1$$
So PDNF corresponding to it is 
$$(p'.q'.r')+(p'.q'.r)+(p'.q.r')+(p'.q.r)+(p.q'.r')+(p.q'.r)+(p.q.r')+(p.q.r)$$
The required normal form is ( if I am not wrong ):-

(p^q^r)v(~p^q^r)v(~p^~q^r)v(p^q^~r)

Once you get the form : (¬p∨¬q∨r)∨(¬p∨¬q∨¬r)
Treat this as (¬p)∨(¬q)∨(r)∨(¬p)∨(¬q)∨(¬r)
And convert the individual literals into minterms.

To convert any variable P to a minterm ,just add :  ^(Qv~Q)^(Rv~R)  to P
That is :P^(Qv~Q)^(Rv~R)And then use the distributive laws.