' version 30-03-2017
' compile with: fbc -s console

Data "ABCD", "CABD", "ACDB", "DACB", "BCDA", "ACBD"
Data "ADCB", "CDAB", "DABC", "BCAD", "CADB", "CDBA"
Data "CBAD", "ABDC", "ADBC", "BDCA", "DCBA", "BACD"
Data "BADC", "BDAC", "CBDA", "DBCA", "DCAB"

' ------=< MAIN >=------

Dim As ULong i,j
Dim As String tmp, missing = chr(0, 0, 0, 0) ' or string(4, 0)

For i = 1 To 23
    Read tmp
    For j = 0 To 3
        missing[j] Xor= tmp[j]
    Next
Next

Print "The missing permutation is : "; missing

' empty keyboard buffer
While Inkey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End