I'm sorry, I seem to be missing your point. Are you saying something like this? 
sub recurse {
  if (grep /A/, @a > 1){ my @c = splice @a, 0, 2; splice @c, 1, 0, (@a
+, @b); }
  if (grep /B/, @b > 1){ my @c = splice @b, 0, 2; splice @c, 1, 0, (@a
+, @b); }
  if (grep /A/, @a == 1){ shift @a; }
  if (grep /B/, @b == 1){ shift @b; }
}

[download]
If so, how would you call it and how would you terminate it?

In reply to Re^2: Spreading out the elements by oko1
in thread Spreading out the elements by Anonymous Monk

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