```
@article{MR30759,
AUTHOR = "Whitehead, J. H. C.",
TITLE = "Combinatorial homotopy. {I}",
JOURNAL = "Bull. Amer. Math. Soc.",
FJOURNAL = "Bulletin of the American Mathematical Society",
VOLUME = "55",
YEAR = "1949",
PAGES = "213--245",
ISSN = "0002-9904",
MRCLASS = "56.0X",
MRNUMBER = "30759",
DOI = "10.1090/S0002-9904-1949-09175-9"
}
```

$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$