Large but killable
Enlarging the eye space eventually buys life — but not every big space is safe. The compact five-point shapes, knife-handle five and this cross five among them, all hide a single point whose occupation leaves the space unable to split: one eye at most, then capture. Even the round six-point flower six dies to its exact centre — the famous exception that has cost whole games. Only genuinely long shapes, from the straight six upward, are beyond a one-point kill, so the rule of thumb is about geometry, not arithmetic: odd and clustered means find the centre; long and thin means relax. This plus-shaped space is the textbook compact five. White to play: strike the vital centre.