Merging multiple, arbitrarily sorted lists into one list

Given 3 lists which are arbitrarily sorted by the same but unknown sort order. Is there an algorithm that merges these lists into one which is then still sorted by the same order? Example: List1: a b c f h List2: b c e h List3: c d e f Assume these lists are sorted but the sort order used is not known. I want to combine these lists to a result that does not contain duplicates but still maintains the sort order: a b c d e f h As said above: It is known, that the given lists are sorted but it is not known by which order, but the requirement is that the merged list is still sorted by the same (unknown) order. In the example above, I know that the element "f" is positioned between "e" and "h" because from List1 I know that "c" < "f" < "h", from List2 I know that "c" < "e" < "h" and from List3 I know that "e" < "f" and "c" < "e" which combines to: "c" < "e" < "f" < "h" If the sort order cannot be determined by any of the given lists, it is permissible to just append the element to the end of the result list. Also, if the sort order of a sequence of elements cannot be determined it is permissible to insert them in any order into the list as long as they are in the right place (e.g. if I know that "b" and "c" must be inserted between "a" and "d" but I don't know if it should be a b c d or a c b d, then both are permissible.) Of course this is just an example. The real lists are longer (but contain less than 100 elements), contain not single but multiple character elements and the sort order is not alphabetic. Also, I have got up to 5 lists. I need to implement this algorithm in Delphi (and no: This is not homework but a real life problem), but I take an algorithm in an language provided it does not contain too much compiler magic or complex library functions. Performance is not much of an issue because this is done once.