@article{RSMUP_1991__86__1_0,
     author = {Sola, Dino},
     title = {Nullification number and flyping conjecture},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {1--16},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {86},
     year = {1991},
     mrnumber = {1154094},
     zbl = {0754.57003},
     language = {en},
     url = {http://archive.numdam.org/item/RSMUP_1991__86__1_0/}
}