Hrqls: what about this figuve ? if white plays at A, then black can play at B, but white can then play at the position left of A ? (or is that not allowed because the white group, then existing of 2 stones, will have no liberties anymore ?)

Hrqls:
Is the K13 group dead? No. If black tries to invade at L13, white would play at M13. Now, black cannot play at L12 or N13, as it would be suicide. The L13 stone is dead and white lives in that area. If black invades at M13, white plays at L13 and a similar thing happens.

Is the M6 stone dead? Yes, if it were played out, white could capture the black stone. But white cannot make two eyes in that area enclosed by black. Since two eyes are the minimum requirement for life, the white stones are dead. It is in white's best interest to not capture that black stone, as white needs to play more than one stone to capture a single stone; the net outcome for white would be less than just declaring them dead.

If white plays at A and black plays at B, white *cannot* play to the left of A. It would be suicide because the black group still has one liberty to the right of B. This is the same situation as the K13 group in your previous question. (except this is straight 4 versus bent 4)

jurek: the K13 group.

ah! i see the outcome :) nice
is it always true then when there is an even empty spaces within a group, then the group is not dead ? if it would have been an odd number of spaces i think the group would be dead ?
(i didnt try it out yet though :))

Hrqls:
is it always true then when there is an even empty spaces within a group, then the group is not dead ? if it would have been an odd number of spaces i think the group would be dead ?

No and no. A group needs two eyes to live: having two eyes prevents the opponent to capture the group since he's not allowed to fill in both eyes at once.
Whether the group can make two eyes or not depends on the internal shape of the group and on whose turn it is. Some shapes with 4 empty intersections are alive, some with 6 empty intersections are dead (when it is the opponent's turn).
For exact shapes see the tutorial, since it is difficult to explain by words only. The tutorial is a couple of interactive lessons.
www.goproblems.com is also a good excercise even for trained players.

Mirjam: thanks .. i hoped to have found a shortcut to a complicated problem ;)

i was halfway the tutorial when i had leave yesterday .. will continue it this evening or tomorrow :)

more questions will come .. be sure of that ;)

jurek: the M6 question
nice!! thats a good thing to remember ... capturing would make it worse indeed :)

thanks for your answers!
i am slowly learning :)