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A yardstick and a blackboard pictured during a mathematics lesson of the third grade class W15d with teacher Jean-Louis Féraud at the gymnasium of the Cantonal School Solothurn, Switzerland, on May 15, 2018. The Cantonal School Solothurn consists of a gymnasium, a specialized upper secondary school (Fachmittelschule FMS) and a secondary school (Sekundarschule P), which prepares the pupils for the gymnasium. (KEYSTONE/Christian Beutler)