DB<33> x @a=(0,1,1); grep { (each @a)[1] } A..L
0  'B'
1  'C'
2  'F'
3  'G'
4  'J'
5  'K'
[download]

here the general case w/o cheating:

(like when the filter cycle ends with a 1 you'd need)

  DB<34> x @a=(0,0,1,1); grep { (each @a)[1] // (each @a)[1] } A..L
0  'C'
1  'D'
2  'G'
3  'H'
4  'K'
5  'L'
[download]