Tsumego from a game.

[Wildclaw]

Sometimes the simplest move is the easiest to overlook:

Talking about simple moves. Looks like no one in here follows the principle presented in Fundamentals of Go, "The first fundamental rule for killing enemy groups is to narrow their eyespace" and "First check the fundamental rule. If it works, you need look no further"

In this case reducing eyespace is enough for black to kill.

$$c
$$ . . . . . . . . . . |
$$ . . . . X X . . . . |
$$ , . X , X O X X X . |
$$ . X . X O 5 O O X . |
$$ . . . 3 O . 4 . O 1 |
$$ . . . . . . . . 2 . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$c
$$ . . . . . . . . . . |
$$ . . . . X X . . . . |
$$ , . X , X O X X X . |
$$ . X . X O 5 O O X . |
$$ . . . 3 O . 4 . O 1 |
$$ . . . . . . . . 2 . |
$$ --------------------+[/go]

Although to be fair, for me, playing 5 as a placement to expand the inner eye is kind of easier to read due to resulting in a common dead l&d position.

$$c
$$ . . . . . . . . . . |
$$ . . . . X X . . . . |
$$ , . X , X O X X X . |
$$ . X . X O 6 O O X . |
$$ . . . 3 O . 4 . O 1 |
$$ . . . . 8 7 9 5 2 . |
$$ --------------------+

Click Here To Show Diagram Code

[go]$$c
$$ . . . . . . . . . . |
$$ . . . . X X . . . . |
$$ , . X , X O X X X . |
$$ . X . X O 6 O O X . |
$$ . . . 3 O . 4 . O 1 |
$$ . . . . 8 7 9 5 2 . |
$$ --------------------+[/go]