Tsumego (Capture) #5309455 (2-move)
Black to play — capture the marked white stones
Capture these stones
Why this move works
The answer is E2 then G2. The three white stones (G1, F1, F2) have liberties at G2 and E2.
Stop E2 first. If you fill G2 first, White extends to E2 and resists. Seal the escape at E2, then fill G2 to capture.