link strings    # for permutes

procedure main()
givens := set![ "ABCD", "CABD", "ACDB", "DACB", "BCDA", "ACBD", "ADCB", "CDAB", "DABC", "BCAD", "CADB",
                "CDBA", "CBAD", "ABDC", "ADBC", "BDCA", "DCBA", "BACD", "BADC", "BDAC", "CBDA", "DBCA", "DCAB"]

every insert(full := set(), permutes("ABCD"))  # generate all permutations
givens := full--givens                         # and difference

write("The difference is : ")
every write(!givens, " ")
end