There has been some debate over the years as to exactly which
  circumstances will trigger a Compost.  The main issue arises because
  it's possible for the card to be black in the graveyard but not when
  it's in the hand, or in play; it's also possible for the card to
  be black in the hand or in play but not in the graveyard.  Under the
  current regime, the trigger event is considered to be a weird mix of
  a leaves-play trigger and an ordinary trigger, so the following 
  results apply:

    Compost  {1}{G}  Enchantment 
  / Whenever a black card is put into an opponent's graveyard, you may
    draw a card.

  Black in opponent's hand, nonblack in opponent's graveyard: No trigger.

  Black in play, nonblack in opponent's graveyard: Trigger.

  Nonblack in opponent's hand, black in opponent's graveyard: Trigger.

  Nonblack in play, black in opponent's graveyard: No trigger.

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