Search for neutral heavy leptons produced in Z decays - Abreu,P; Adam,W; Adye,T; Ajinenko,I; Alekseev,GD; Alemany,R; Allport,PP; Almehed,S; Amaldi,U; Amato,S; Andreazza,A; Andrieux,ML; et al. (ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS, 1997)