si tu as 0 cartes tu peux pas piocher donc la question se pose pas. tu peux pas remplacer la pioche par le dragage vu que tu as rien a remplacer.
si tu as qiue 4 cartes ben tu peux pas operer un dredge 6.
Citation :
702.49a Dredge is a static ability that functions only while the card with dredge is in a player's graveyard. "Dredge N" means "As long as you have at least N cards in your library, if you would draw a card, you may instead put N cards from the top of your library into your graveyard and return this card from your graveyard to your hand."