C.H. Dowker had characterised these spaces in 1951 as those normal spaces for which the product with the unit interval is not normal, and asked whether any such space existed. M.E. Rudin constructed an example in 1971, and Zoltán Balogh gave the first ZFC construction of a small (cardinality continuum) example.
- C.H. Dowker, On countably paracompact spaces, Can. J. Math. 3 (1951) 219-224. Zbl. 0042.41007
- M.E. Rudin, A normal space X for which X × I is not normal, Fundam. Math. 73 (1971) 179-186. Zbl. 0224.54019
- Z. Balogh, A small Dowker space in ZFC, Proc. Amer. Math. Soc. 124 (1996) 2555-2560. Zbl. 0876.54016