Bxb3 answered by axb3++ as per previous answer.

4 a4 is answered by the delaying move Ba2, which means mate in 6 i guess. 

if 4...Bxb3 then 5.axb3#. And for 4.a4 Ba2 postpones the mate for another move because then the a4 pawn will be hanging.

Ok, I completely missed the discovered check(mate). Thanks.

What if Black plays Kc5 instead of taking the Knight?

hmm:)

very nice

nice

I think black might have had better moves along the way. 4. ... Rfc8 (preventing 5.Bc7# but allowing 5.Bd2#) seemed pretty insipid, but at that point there was no way to prevent 5.checkmate.

3. ... K captures the Knight at a5 may have been necessary, but it blocked the king onto one column.   3. ... Kc5 might have been better.

Edit:  marmaladecat  has shown that 3. ... Kc5 still ends in forced mate in 5.

good one

 How on earth does a 2000-rated player ask this question?

jflint wrote; What if Black plays Kc5 instead of taking the Knight?

3...Kc5 is met by 4.Rd1, trapping the Black king and giving White 3 ways to mate next move; Black can't stop all of them.

Not bad

 First attempt at this.  Was not too shabby.

i think it is a medium puzzle cuz i needed hel for it :/

Nice one.

Now that's a proper and awesome puzzle!

fourth was hard. 

They should allow alternates...

Nice puzzle.