@article{Welch1966, 
     author = "Welch, John T.", 
     doi = "10.1145/321328.321331", 
     issn = "00045411", 
     journal = "Journal of the ACM", 
     link = "http://portal.acm.org/citation.cfm?doid=321328.321331", 
     month = "apr", 
     number = "2", 
     pages = "205--210", 
     title = "A Mechanical Analysis of the Cyclic Structure of Undirected Linear Graphs", 
     uri = "http://portal.acm.org/citation.cfm?doid=321328.321331", 
     volume = "13", 
     year = "1966", 
}

Problems: 421