▁voices ▁may ▁enter ▁either ▁simultaneously ▁or ▁success ively . ▁If ▁voices ▁extend ▁the ▁rh yth mic ▁values ▁of ▁the ▁leader ▁( for ▁example , ▁by ▁dou bling ▁all ▁note ▁values ), ▁a ▁procedure ▁known ▁as ▁augment ation , ▁the ▁resulting ▁canon ▁can ▁be ▁called ▁an ▁augment ation ▁canon ▁or ▁canon ▁by ▁augment ation ▁( can on ▁per ▁augment ation em ) ▁or ▁sl oth ▁canon ▁( rec alling ▁the ▁slow ▁movement ▁of ▁the ▁sl oth ). ▁Con vers ely , ▁if ▁they ▁reduce ▁the ▁note ▁values ▁in ▁dimin ution , ▁it ▁can ▁be ▁called ▁a ▁dimin ution ▁canon ▁or ▁canon ▁by ▁dimin ution ▁( can on ▁per ▁dimin ution em ). ▁▁ ▁Pro lation ▁can ons ▁are ▁among ▁the ▁most ▁difficult ▁can ons ▁to ▁write , ▁and ▁are ▁relatively ▁rare ▁in ▁the ▁re pert ory , ▁though ▁they ▁are ▁most ▁common ▁in ▁the ▁early ▁Renaissance ▁and ▁from ▁the ▁ 2 0 th ▁century ▁to ▁the ▁present . ▁Ex amples ▁of ▁pro lation ▁can ons ▁from ▁the ▁Renaissance ▁include ▁Le ▁Ray ▁Au ▁So ley l ▁by ▁Johannes ▁C icon ia ▁( late ▁ 1 4 th ▁century ); ▁the ▁entire ▁Miss a ▁pro lation um ▁by ▁Johannes ▁O ck eg hem ▁( mid - 1 5 th ▁century ), ▁in ▁which ▁each ▁separate ▁section ▁of ▁the ▁mass ▁expl ores ▁a ▁different ▁pro lation ▁( or ▁different ▁gap ▁between ▁entries ▁and ▁relative ▁speed ▁of ▁each ▁voice ); ▁the ▁Ag n us ▁De i ▁from ▁the ▁Miss a ▁L ' homme ▁arm é ▁super ▁voc es