Could somebody recommend me a book with some advanced Excel functions. I
don't need a book for beginners and I don't need a book that repeats simple
functions discribed in free Excel help menu.
e.g. I found this formula recently
"=SUMPRODUCT(--(B1:B100=1),--(F1:F100="Done"))" and I wish I found it a
couple of months ago. I knew the "sumproduct" formula, but I did not know
that it could be used this way (I still don't know what "--" means).
So, maybe somebody knows a book about Excel with interesting problems and
advanced ways to solve them.

Thank you,

Evgeny