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Happy #Birthday South African mathematician, Francis Guthrie! Read about him & the Four-Colour Problem http://t.co/W5ArZtIgVi
Happy #Birthday South African mathematician, Francis Guthrie! Read about him & the Four-Colour Problem http://t.co/W5ArZtIgVi
Happy #Birthday South African mathematician, Francis Guthrie! Read about him & the Four-Colour Problem http://t.co/W5ArZtIgVi