@article { SZHR11, title = {Drawing Euler Diagrams with Circles: The Theory of Piercings}, journal = {IEEE Transactions on Visualization and Computer Graphics}, month = {jul}, number = {7}, pages = {1020-1032}, url = {http://www.computer.org/portal/web/csdl/doi/10.1109/TVCG.2010.119}, year = {2011}, author = {Stapleton, Gem and Zhang, Leishi and Howse, John and Rodgers, Peter} }