Watch out of you use @Contains
@Contains is a nice Lotus Formula language function, which determines whether a substring is stored within a string.
In theory. If you are using Notes 6.5.5 and are working with non-ASCII characters you are in trouble. As Hans-Peter Kuessner blogs, if the string to search contains an Umlaut, it always returns true.
This regression-bug will probably be fixed in 6.5.6.