The Sedentary Multi-Frequency Survey of HBL BL Lacs an Update

New results from the Sedentary Multi-Frequency Survey of HBL BL Lacs (Giommi, Menna and Padovani 1999) are presented. The survey, which is based on a highly efficient (>80%) multi-frequency statistical selection method and includes 155 objects, is currently spectroscopically identified at the 83% level and is the largest flux limited and complete sample of BL Lacs existing today. Here we report on updated results on the radio LogN-LogS and the Ve/ Va test together with a preliminary version of the radio luminosity function. Our results (<Ve / Va > = 0.41 ± 0.02) confirm the negative cosmological evolution of HBL BL Lacs at low radio fluxes (fr about 3.5-20 mJy) and set important constraints to emission models and Blazar unification schemes. We also present BeppoSAX observations of 4 BL Lacs of the Sedentary Survey which confirm that the Spectral Energy Distributions (SEDs) of these sources are typical of extreme HBL BL Lacs.