Could someone help me on the following?

Column A contains a list of string values and so does column C. The
strings in both columns have corresponding numerical values in columns
B and D. I need a routine (macro?) that cheks if a certain string
exists in both columns A and C.If the same string is found in both,
nothing else is done and if a certain
string is only found in column C, that string and the corresponging
value in column D are deleted. The procedure should be repeated until
the lists contain the only the same strings. In other words the goal is
that both lists would become identical, ie the strings in column C
missing from column A would be deleted.


Thanks,
jarmo