In this paper we represent every lattice by subgroups of free groups using the concept of the homotopy group of a graph.
@article{119077, author = {Ji\v r\'\i\ T\r uma}, title = {Representing lattices by homotopy groups of graphs}, journal = {Commentationes Mathematicae Universitatis Carolinae}, volume = {40}, year = {1999}, pages = {215-221}, zbl = {0977.06003}, mrnumber = {1732642}, language = {en}, url = {http://dml.mathdoc.fr/item/119077} }
Tůma, Jiří. Representing lattices by homotopy groups of graphs. Commentationes Mathematicae Universitatis Carolinae, Tome 40 (1999) pp. 215-221. http://gdmltest.u-ga.fr/item/119077/
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