Confused on how to do a simple discrete math problem

[n00by]

Homework Statement

Use the equivalence $p\rightarrow(r \rightarrow s) \equiv p\wedge r\rightarrow s$ to rewrite the following problem before the proof.

Homework Equations

$[p\rightarrow (q\rightarrow r)]\wedge (p\rightarrow q) \tautologicallyimplies (p\rightarrow r)$

The Attempt at a Solution

$[p\rightarrow (q\rightarrow r)]\wedge (p\rightarrow q) \tautologicallyimplies (p\rightarrow r)$

1. $p\rightarrow (q\rightarrow r) \equiv p\wedge q \rightarrow r \equiv \neg p \vee \neg q \vee r$
2. $p\rightarrow q \equiv \neg p \vee q$

3. $(\neg p \vee q)\wedge (\neg p \vee \neg q \vee r) \equiv ... \equiv p \rightarrow q\wedge r$

What am I doing wrong?

Thanks!

 

[n00by]

Does anyone know how to do this proof?

 

[alanlu]

Go back to (p and q) -> r. What does p -> q say about the logical value of (p and q)?