@article{10_4153_CJM_1989_011_7,
     author = {Porter, Jack R. and Woods, R. Grant},
     title = {The {Poset} of {Perfect} {Irreducible} {Images} of a {Space}},
     journal = {Canadian journal of mathematics},
     pages = {213--233},
     year = {1989},
     volume = {41},
     number = {2},
     doi = {10.4153/CJM-1989-011-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1989-011-7/}
}