Bibtex of String / Parenthesis

@article{Er1983, 
     author = "Er, M. C.", 
     doi = "10.1093/comjnl/26.3.205", 
     issn = "0010-4620", 
     journal = "The Computer Journal", 
     link = "http://comjnl.oupjournals.org/cgi/doi/10.1093/comjnl/26.3.205", 
     month = "mar", 
     number = "3", 
     pages = "205--207", 
     title = "A Note on Generating Well-Formed Parenthesis Strings Lexicographically", 
     uri = "http://comjnl.oupjournals.org/cgi/doi/10.1093/comjnl/26.3.205", 
     volume = "26", 
     year = "1983", 
}

@article{Walsh1998, 
     author = "Walsh, Timothy R.", 
     doi = "10.1006/jagm.1998.0960", 
     issn = "01966774", 
     journal = "Journal of Algorithms", 
     link = "http://www.sciencedirect.com/science/article/pii/S0196677498909609 http://linkinghub.elsevier.com/retrieve/pii/S0196677498909609", 
     month = "oct", 
     number = "1", 
     pages = "165--173", 
     title = "Generation of Well-Formed Parenthesis Strings in Constant Worst-Case Time", 
     uri = "http://www.sciencedirect.com/science/article/pii/S0196677498909609", 
     volume = "29", 
     year = "1998", 
}