> The only condition is that an even number must have an all blue flipside. This condition is either irrelevant or satisfied for the blue card. For all other ca

> The only condition is that an even number must have an all blue flipside. This condition is either irrelevant or satisfied for the blue card. For all other cards, we don't know. The card with "1" may have the number "4" on the flip side. So we need to check ask other cards. Very good point, thank you. I have added an explicit statement that cards are consistent.