Abstract Performance 

Sorcery
Exile the top four cards of your library in a face-down pile, then exile the top four cards of your library in a face-up pile. An opponent chooses one of those piles. Put that pile into your graveyard. Look at the cards in the other pile. You may cast a spell from among them without paying its mana cost. Put the rest into your hand.
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Cards that do something similar expected a card that isn't here?
Reports become test cases the matcher is graded against before an update ships. Delvefall isn't a chatbot guessing, it compares the printed rules text of every card with plain math, and examples like yours decide which differences should count.