Dim PList as QStringList
PList.addItems "ABCD", "CABD", "ACDB", "DACB", "BCDA", "ACBD", "ADCB", "CDAB"
PList.additems "DABC", "BCAD", "CADB", "CDBA", "CBAD", "ABDC", "ADBC", "BDCA"
PList.additems "DCBA", "BACD", "BADC", "BDAC", "CBDA", "DBCA", "DCAB"

Dim NumChar(4, 65 to 68) as integer
Dim MPerm as string

'Create table with occurences
For x = 0 to PList.Itemcount -1
    for y = 1 to 4
        Inc(NumChar(y, asc(PList.Item(x)[y])))
    next
next

'When a char only occurs 5 times it's the missing one
for x = 1 to 4
    for y = 65 to 68
        MPerm = MPerm + iif(NumChar(x, y)=5, chr$(y), "")
    next
next

showmessage MPerm
'= DBAC