Four die, six live
This is a continuation of the discussion given in
Six die, eight live (on the second line,)
but applies to a group on the second line that has a base at the edge of the board.
Here White will die even if White plays first.
1 is the only move, and Black 2 will kill the group. Of course, if Black ignores
White 1, White can play at 2 and make two eyes.
Six with a base in the corner is unconditionally alive.
If Black tries to reduce the white eye-space, white will still have four in a row.
and how about five?
When there are five stones, if White plays first, White will live: if Black plays first,
White will die. If you have read the "Six die, eight live" article you can work this
out for yourself.