Bibtex of Permutation / Set

@article{Dershowitz1975, 
     author = "Dershowitz, Nachum", 
     doi = "10.1007/BF01932689", 
     issn = "00063835", 
     journal = "BIT", 
     keyword = "loop-free algorithms,ordering,permutation generation,permutations,permutations and combinations", 
     link = "http://link.springer.com/10.1007/BF01932689", 
     month = "jun", 
     number = "2", 
     pages = "158--164", 
     title = "A simplified loop-free algorithm for generating permutations", 
     uri = "http://link.springer.com/10.1007/BF01932689", 
     volume = "15", 
     year = "1975", 
}

@article{Ehrlich1973a, 
     author = "Ehrlich, Gideon", 
     doi = "10.1145/321765.321781", 
     issn = "00045411", 
     journal = "Journal of the ACM", 
     link = "http://dl.acm.org/citation.cfm?id=321765.321781", 
     month = "jul", 
     number = "3", 
     pages = "500--513", 
     publisher = "ACM", 
     title = "Loopless Algorithms for Generating Permutations, Combinations, and Other Combinatorial Configurations", 
     uri = "http://dl.acm.org/citation.cfm?id=321765.321781", 
     volume = "20", 
     year = "1973", 
}