Thanks for feedback

How about no buttons at all, and instead of an option to "shuffle" a pack, lets show up cards in random order. The more often they are set to known, the less often they show up. Once they are not corretly answered they are set back to zero - which means: shown often again.
Another idea of saving space and having some more options is to use a special region of the card for flipping to back side only (maybe a dog-ear shows that the card has another side, that region is for flipping).
The rest of the body could be used in various ways, like watermark symbols that are fairly visible (green thumb up for known, red thumb down for not known) but remind that there is something to do when pressing that region. Once pressed the watermark becomes highlighted an the choice is made.
third idea: sliding cards up: means i knew it, sliding it down, get back one step.
fourth idea: the buttons green / red automatically are added to the back side of each card. Either on top or at the end of the card right after / before the card text.
Glad my ideas are appreciated
