Summoning Trap
Instant — Trap
If a creature spell you cast this turn was countered by a spell or ability an opponent controlled, you may pay 
rather than pay this spell's mana cost.
Look at the top seven cards of your library. You may put a creature card from among them onto the battlefield. Put the rest on the bottom of your library in any order.
Kieran Yanner
Modern Masters 2017 (MM3)
• #139Rulings
Casting a Trap by paying its alternative cost doesn't change its mana cost or mana value. The only difference is the cost you actually pay.
(wotc • 2009-10-01)
Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.
(wotc • 2009-10-01)
You may ignore a Trap's alternative cost condition and simply cast it for its normal mana cost. This is true even if its alternative cost condition has been met.
(wotc • 2009-10-01)
If there are seven or fewer cards in your library, you'll look at all of them.
(wotc • 2009-10-01)
Rulings
Casting a Trap by paying its alternative cost doesn't change its mana cost or mana value. The only difference is the cost you actually pay.
(wotc • 2009-10-01)
Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.
(wotc • 2009-10-01)
You may ignore a Trap's alternative cost condition and simply cast it for its normal mana cost. This is true even if its alternative cost condition has been met.
(wotc • 2009-10-01)
If there are seven or fewer cards in your library, you'll look at all of them.
(wotc • 2009-10-01)