Tome of Stolen Knowledge

Tome of Stolen Knowledge enters the battlefield
with three page counters on it.
{u/b}{u/b}{t}: Remove a page counter from Tome of
Stolen Knowledge. Look at the top three cards of target player's library. Exile up to one instant or sorcery card from among them face down. Put the
rest on the bottom of that player's library in any
order. For as long as that card remains exiled, you
may look at it, you may cast it, and you may spend
mana as though it were mana of any type to cast
that spell.