@article{10_4153_S0008414X21000614,
     author = {Guzm\'an, Osvaldo},
     title = {The ultrafilter number and $\mathfrak {hm}$},
     journal = {Canadian journal of mathematics},
     pages = {494--530},
     year = {2023},
     volume = {75},
     number = {2},
     doi = {10.4153/S0008414X21000614},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/S0008414X21000614/}
}