Sh:28

Bib entry
@article{Sh:28,
 author = {Shelah, Saharon},
 title = {{There are just four second-order quantifiers}},
 journal = {Israel J. Math.},
 fjournal = {Israel Journal of Mathematics},
 volume = {15},
 year = {1973},
 pages = {282--300},
 issn = {0021-2172},
 doi = {10.1007/BF02787572},
 mrclass = {02B15},
 mrnumber = {0335237},
 mrreviewer = {J. A. Makowsky},
 doi = {10.1007/BF02787572}
}