did not ruin, or spoil anything at all, thank you for pointing out Ra7

I was thinking Black draws?

And sorry if it spoils the solution. 

Still getting the hang of this position editor. I couldn't nest any subvariations. 

If 1....Ra7 immediately, not 2. Re1? Rd7+. Instead, 2. Re6. Then white can meet 2....Rd7+ with 3. Rd6, or 2...Kb5 with Rb6+.

yes a-pawn on 6th rank, got it, inserted diagram from what you described,

see

and what if Rook does not capture a-pawn, draw?

? That is a white a-pawn, no? 2...Rxd6 loses the rook. But with the knight on d6, white can't defend the a-pawn with Re6. So it seems natural to go after the a-pawn with 2...Ra7. 

wait, let me try, mmmmk

uhmm

uhmmmm never looked at that Ra7?,

you mean Rh7

I like how the puzzle involves multiple themes. White can threaten to protect the pawn and consolidate (with Re6), win the rook, or mate black on the side of the board. One sideline is 2...Ra7 instead of 2...Rd6. Then I suppose the idea is 3. Re1! Rxa6 4.Rb1+ Ka5 5. Kc5

it is the work of Dr John Nunn, dont know if I told you about his books? I dont have them, but I have come across them, never read anything from him, yet

articles are here, bob

http://chessbase.com/newsdetail.asp?newsid=8117

and

http://www.chessbase.com/newsdetail.asp?newsid=7279

they have this composed puzzle competition

yup..both surprised me

you can try with this,

http://www.shredderchess.com/online-chess/online-databases/endgame-database.html

bob, white must make the best, it is ahead

the composed puzzle here show two unexpected moves

first, moving in between the N and R,

second, to allow the Knight capture,

this is very cute..i didnt get it, but i think it shows why you say learn the end game first :)