Some lines not broken in BibLaTeX bibliography

Question

Some entries in my bibliography cause Overfull \hboxes for reasons I don't understand. Here are examples:

The above example was fixed by allowing the ISBN to break with \-, but I can't figure out what's wrong with the example below:

This is my main file:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{import}

\usepackage[
    backend=biber,
    style=alphabetic,
    citestyle=alphabetic,
    sorting=nyt
]{biblatex}
\addbibresource{refs.bib}

\begin{document}

    \nocite{*}
    \printbibliography[title={References}]\label{sec:paperrefs}

\end{document}

And refs.bib:

@inproceedings{Cook1971,
    author = {Cook, Stephen A.},
    title = {The Complexity of Theorem-Proving Procedures},
    year = {1971},
    isbn = {9781450374644},
    publisher = {Association for Computing Machinery},
    address = {New York, NY, USA},
    url = {https://doi.org/10.1145/800157.805047},
    doi = {10.1145/800157.805047},
    booktitle = {Proceedings of the Third Annual ACM Symposium on Theory of Computing},
    pages = {151–158},
    numpages = {8},
    location = {Shaker Heights, Ohio, USA},
    series = {STOC ’71}
}

@InCollection{sep-computational-complexity,
    author       =  {Dean, Walter},
    title        =  {Computational Complexity Theory},
    booktitle    =  {The Stanford Encyclopedia of Philosophy},
    editor       =  {Edward N. Zalta},
    howpublished =  {\url{https://plato.stanford.edu/archives/spr2017/entries/computational-complexity/}},
    year         =  {2017},
    edition      =  {Spring 2017},
    publisher    =  {Metaphysics Research Lab, Stanford University}
}

@misc{Friedman2002,
    author = "E. Friedman",
    title  = "Pushing blocks in gravity is NP-hard",
    year   = "2020"
}

@article{Garey1976,
    title={The Planar Hamiltonian Circuit Problem is NP-Complete},
    author={M. R. Garey and David S. Johnson and Robert E. Tarjan},
    journal={SIAM J. Comput.},
    year={1976},
    volume={5},
    pages={704-714}
}

@inproceedings{Demaine2001,
    title={Pushing blocks is np-complete for noncrossing solution paths},
    author={Erik D. Demaine and Michael Hoffmann},
    booktitle={CCCG},
    year={2001}
}

@phdthesis{Uehara1998,
    title    = {Probabilistic Algorithms and Complexity Classes},
    school   = {Department of Computer Science and Information Mathematics, The University of Electro-Communications},
    author   = {R. Uehara},
    year     = {1998}
}

@inproceedings{Uehara1990,
    title={Generalized Hi-Q is NP-Complete},
    author={Ryuhei Uehara and Shigeki Iwata},
    year={1990}
}

@article{Ravikumar2004,
    title = "Peg-solitaire, string rewriting systems and finite automata",
    journal = "Theoretical Computer Science",
    volume = "321",
    number = "2",
    pages = "383 - 394",
    year = "2004",
    issn = "0304-3975",
    doi = "https://doi.org/10.1016/j.tcs.2004.05.005",
    url = "http://www.sciencedirect.com/science/article/pii/S0304397504003688",
    author = "B Ravikumar",
    keywords = "Peg-solitaire, String rewriting system, Length-preserving, Change-bounded rewriting rule",
    abstract = "We consider a class of length-preserving string rewriting systems and show that the set of encodings of pairs of strings 〈s,f〉 such that f can be derived from s using the rewriting rules can be accepted by finite automata. As a consequence, we show the existence of a linear time algorithm for determining the solvability of a given k×n peg-solitaire board, for any fixed k. This result is in contrast to the results of (13) and (1) that the same problem is NP-hard for n×n boards. We look at some related string rewriting systems and find conditions under which the encodings of the pairs 〈s,f〉 where f can be derived from s is regular."
}

@article{Plesnk1979,
    title={The NP-Completeness of the Hamiltonian Cycle Problem in Planar Digraphs with Degree Bound Two},
    author={J{\'a}n Plesn{\'i}k},
    journal={Inf. Process. Lett.},
    year={1979},
    volume={8},
    pages={199-201}
}

@Book{GPC,
    AUTHOR        = {Robert A. Hearn and Erik D. Demaine},
    TITLE         = {Games, Puzzles, and Computation},
    PUBLISHER     = {A K Peters},
    MONTH         = {July},
    YEAR          = {2009},
    length        = {250 pages}
}

@article{Turing1937,
    title={Computability and λ-definability},
    volume={2},
    DOI={10.2307/2268280},
    number={4},
    journal={Journal of Symbolic Logic},
    publisher={Cambridge University Press},
    author={Turing, A. M.},
    year={1937},
    pages={153–163}
}

The Overfull hboxes don't happen if I cite only the Cook1971 entry.

Related questions are usually about URLs, but most URLs in my bibliography seem to break correctly.

Why does this happen, and how can I force my bibliography entries back into text margins?

Answer 1

The MWE doesn't reproduce the badly broken ISBN for me and the issue in Uehara1990 is much less pronounced. But be that as it may.

• The issue with the ISBN is that TeX simply does not hyphenate numbers by default. An easy workaround that is arguably more aesthetically pleasing anyway would be to put isbn = {978-1-4503-7464-4}, instead of isbn = {9781450374644}, because then TeX can break the ISBN at the hyphens (I used the Library of Congress ISBN Converter from http://www.loc.gov/publish/pcn/isbncnvt_pcn.html). This may not help in all cases, but it should make the situation much better, since it introduces four new break points.

  Note that you don't even have to insert the hyphens yourself. Biber's option --isbn-normalise can do that for you: Automatically validate and format ISBNs.

• One issue with Uehara1990 is that TeX only allows breaks in hyphenated words at the hyphens and nowhere else, so NP-Complete can only be broken as NP-|Complete (and not NP-|Com|plete as you might expect/hope). See for example https://texfaq.org/FAQ-nohyph, Why can words with hyphen char not be hyphenated?, Adequate hyphenation of words already containing a hyphen (these posts also discuss workarounds; just as a complete this answer I realise that barbara beeton suggests NP-\hspace{0pt}Complete in the comments).

Allowing TeX to break the ISBN and NP-Complete massively increases the chance that you get a more nicely broken bibliography, but there is no guarantee that it works in all situations and manual interventions are hard in the bibliography. In How to adjust the breaking in the bibliography? I discuss several methods to improve line breaking in the bibliography.