p = toSet[trim[splitLines["""ABCD
                    CABD
                    ACDB
                    DACB
                    BCDA
                    ACBD
                    ADCB
                    CDAB
                    DABC
                    BCAD
                    CADB
                    CDBA
                    CBAD
                    ABDC
                    ADBC
                    BDCA
                    DCBA
                    BACD
                    BADC
                    BDAC
                    CBDA
                    DBCA
                    DCAB"""]]]

s = ["A","B","C","D"]
for n = s.lexicographicPermute[]
{
   str = join["", n]
   if ! p.contains[str]
      println[str]
}