Double sente yose is large. black1 in right picture is double sente yose, and has 6 point.
It was named "koskos", because either move are called kosum.

Make a sagari at yose after thinking about sente-gote.

This proverb is smile_ace's original.

It was moved from all black1 in 3 pictures.The results of each are

[Figure A] white won 1 point. black 29 points white 30 points
[Figure B] black won 4 points. black=31 points white=27 points
[Figure C] black won 3 points. black=29 points white=26 points

For black, it's the disadvantage result at figure A.

[figure A]
In this case black3 (sagari) is a bad move, because it makes white4 sente. So, at bottom side white can take a sente.
[Figure B]
White took a move white4, becase black3 had next large move (black6).
So, black could take a move black7, and black won 4 points.
[Figure C]
This is the best moves each other.
White took a big move white4 at lower side, because black had taken a big move black1 at upper side. Black took a move black7 with sente, and took a move black13. After all, Black won 3 points.