list all the presidents of the school which had atleast one of the president as society of the sisters of saint ursula of the blessed virgin ?
SELECT DISTINCT var_uri where brack_open var_x dbo_president dbr_Society_of_the_Sisters_of_Saint_Ursula_of_the_Blessed_Virgin sep_dot var_x dbo_president var_uri sep_dot var_x a dbo_School brack_close