@article{10_4153_CMB_1978_085_2,
     author = {Day, Alan},
     title = {Idempotents in {The} {Groupoid} of all {SP} {Classes} of {Lattices}},
     journal = {Canadian mathematical bulletin},
     pages = {499--501},
     year = {1978},
     volume = {21},
     number = {4},
     doi = {10.4153/CMB-1978-085-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1978-085-2/}
}