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2. Charles C. Bonwell and James A. Eison. 1991. Active Learning: Creating Excitement in the Classroom. In ASHEERIC Higher Education Report No. 1 George Washington University Washington DC. Charles C. Bonwell and James A. Eison. 1991. Active Learning: Creating Excitement in the Classroom. In ASHEERIC Higher Education Report No. 1 George Washington University Washington DC.
3. Albert E. Bosman. 2004. Pythagoras Tree reprinted in Bruno Ernst: Bomen van Pythagoras - Variaties van Jos de Mey Aramith Uitgevers Amsterdam 1985. Albert E. Bosman. 2004. Pythagoras Tree reprinted in Bruno Ernst: Bomen van Pythagoras - Variaties van Jos de Mey Aramith Uitgevers Amsterdam 1985.