actually first my friend showed this puzzle to me and i posted it but i never knew it was from a book .sorry to all!!!
Ah, okay. So, you just meant that it is the first puzzle that you posted.
I was just asking why you claimed it as your own, and not accusing you of stealing. Try to ignore what 'Chairman' thinks I said. I just wanted recognition for the creator of the puzzle.
Now, we have learned that this puzzle was created by one Philip Stamma.
I'm thinking that the author may have known the theory, that it's possible for a lone knight to mate, if the other side has a rook pawn, and then constructed the puzzle based on that knowledge. or he may have even been thinking, set up the mate position, and then worked backwards. if the exact puzzle has been posted before by someone else, even that in itself doesn't mean the submitter didn't actually do some creative thinking to duplicate the work.
of course, if you could find where you are "sure" that you saw this before, and post the reference and the original author, and the starting position was exactly the same, that would cast things in a different light.
in any case, I enjoyed working out the solution. so thanks for posting.