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@article{TM2_2011_XIV_1_a3, author = {Borislav Lazarov}, title = {Teaching envelopes in secondary school}, journal = {The Teaching of Mathematics}, pages = {45 }, publisher = {mathdoc}, volume = {XIV}, number = {1}, year = {2011}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TM2_2011_XIV_1_a3/} }
Borislav Lazarov. Teaching envelopes in secondary school. The Teaching of Mathematics, XIV (2011) no. 1, p. 45 . http://geodesic.mathdoc.fr/item/TM2_2011_XIV_1_a3/