PG29: Cancel: Cancel abilities are extremely powerful. Whenever a card is canceled, all text on the card is ignored, and the owner’s fnal attack and defense value are considered zero. Note that the numbers may not be modifed above zero and that a canceled card’s strength cost is not reduced (in other words, the canceled card must still be paid for in strength by its combatant).
On round 1 I play 'Concentrate' (+2 attack and +2 defense on the next turn). On the next turn I play a card that get's cancelled. I would have thought that despite my second card being cancelled, I still gain the +2 attack and +2 defense from the 'Concentrate' I played in round 1, therefore my round 2 attack and defense would both be 2. However, the rule above does explicitly state 'Note that the numbers may not be modifed above zero'. This seems VERY powerful to me, since cancelling a card in this circumstance effectively also cancels the text on the previous card!