src/HOL/Analysis/document/root.bib

+@article{dugundji,
+  author	= {J. Dugundji},
+  title		= {An extension of {Tietze's} theorem},
+  journal	= {Pacific J. Math.},
+  pages		= {353-367},
+  volume  = 1,
+  number  = 3,
+  year    = 1951,
+  url     = {https://projecteuclid.org/euclid.pjm/1103052106}}
+
+@misc{dummy}