FindString.oz

fun {Prefix L1 L2}
  case L1
  of H|T then
    if H == L2.1 then {Prefix T L2.2}
    else false end
  [] nil then true
  end
end

fun {FindString L1 L2}
  case L2
  of H|T then
    if L1.1 == H then {Prefix L1 L2}
    else {FindString L1 T} end
  [] nil then
    if L1 == nil then true
    else false end
  end
end

perfect!