updates opposite to step 1
_two . second = ( _two . second + 1 ) % size2 ; if ( _two . second == 0 ) _two . first = ( _two . first + 1 ) % size2 ; } else { cout << " [ " << a2 [ _one . second ] << " , ▁ " << a1 [ _one . first ] << " ] ▁ " ;