Reference:

Javier Esparza, Pradeep Kanade, and Stefan Schwoon. A negative result on depth-first unfoldings. Software Tools for Technology Transfer, 10(2):161–166, 2008.

Suggested BibTeX entry:

@article{EKS08,
    author = {Javier Esparza and Pradeep Kanade and Stefan Schwoon},
    journal = {Software Tools for Technology Transfer},
    number = {2},
    pages = {161--166},
    title = {A Negative Result on Depth-First Unfoldings},
    volume = {10},
    year = {2008}
}