checking string in string



Hi!
How to check if my dword from param txt1:dword is in sth like that "TXT2 db
50 dup(0)" ?
Eg now txt1 is "ab" and txt2 is "hhaBababggg". How to check if txt1 is in
txt2... I only need to know if it is, not how many times.
How to make this non case sensitive? How to make all letters lower?

Thank You for advice


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