Bibtex of String / Lyndon word

@article{Sawada2003, 
     author = "Sawada, Joe and Ruskey, Frank", 
     doi = "10.1016/S0196-6774(02)00286-9", 
     issn = "01966774", 
     journal = "Journal of Algorithms", 
     keyword = "basis,free lie algebra,generate,lyndon bracket,lyndon word,nth homogeneous component", 
     link = "http://linkinghub.elsevier.com/retrieve/pii/S0196677402002869", 
     month = "jan", 
     number = "1", 
     pages = "21--26", 
     title = "Generating Lyndon Brackets.", 
     uri = "http://linkinghub.elsevier.com/retrieve/pii/S0196677402002869", 
     volume = "46", 
     year = "2003", 
}

@article{Sawada2013, 
     author = "Sawada, Joe and Williams, Aaron", 
     doi = "10.1016/j.tcs.2012.01.013", 
     issn = "03043975", 
     journal = "Theoretical Computer Science", 
     month = "Sep", 
     pages = "46--54", 
     publisher = "Elsevier", 
     title = "A Gray code for fixed-density necklaces and Lyndon words in constant amortized time", 
     volume = "502", 
     year = "2013", 
}