mergeI i0 i1 = if l0<=l1 then mergeI' i0 l0 i1 l1 else mergeI' i1 l1 i0 l0
  where
    l0 = length i0
    l1 = length i1
mergeI i0 i1 = if l0<=l1 then mergeI' i0 l0 i1 l1 else mergeI' i1 l1 i0 l0
  where
    l0 = length i0
    l1 = length i1
mergeI i0 i1 = if l0<=l1 then mergeI' i0 l0 i1 l1 else mergeI' i1 l1 i0 l0
  where
    l0 = length i0
    l1 = length i1