the union internationale des associations d'alpinisme defines a summit in the alps as independent, if the connecting ridge between it and a higher summit drops at least 30 m (a prominence/drop of 30 m, with the lowest point referred to as the "key col"). there are over 3300 such summits exceeding 2500 m in switzerland alone. in order for a peak to qualify as an independent mountain, traditionally a prominence of at least 300 m, or 10 times the aforementioned criterion value, has been used. inclusion based on prominence is expedient for its objectivity and verifiability, but has its drawbacks. for example, an impressive mountain peak dominating a valley may be connected via long high ridges to a barely higher hidden summit. among the better-known peaks absent from this list are aiguille du dru (due to aiguille verte), dent du géant (grandes jorasses), mont blanc de cheilon (ruinette), nadelhorn and täschhorn (dom), piz d'err (piz calderas), piz badile (piz cengalo), piz palü (piz zupo), similaun (hintere schwarze), crozzon di brenta (cima tosa), and cimon della pala (cima vezzana).