@article {FrVe97a,
AUTHOR = {Friedman, Sy D. and Veli{\v{c}}kovi{\'c}, Boban},
TITLE = {{$\Delta\sb 1$}-definability},
JOURNAL = {Ann. Pure Appl. Logic},
FJOURNAL = {Annals of Pure and Applied Logic},
VOLUME = {89},
YEAR = {1997},
NUMBER = {1},
PAGES = {93--99},
}