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| 1992 | ||
|---|---|---|
| 2 | Piet Hein: We shall have to evolve problem solvers galore Since each problem we solve creates ten problems more. Discrete Mathematics 100(1-3): 221 (1992) | |
| 1 | Piet Hein: Problems worthy of attack prove their worth by hitting back. Discrete Mathematics 100(1-3): 3 (1992) | |