 One of the tenets of right hand technique in melody playing is strict alternation of i & m. That is, no right hand finger should be used twice in a row (excluding the thumb).The a finger is occasionally used if i-m alternation creates an awkward string-crossing in the right hand.Otherwise, the default is strict alternation of i & m. Where the a finger is used, i-a or a-m fingering is preferred to m-a, due to the physical constraints of the hand.