this program is meant to used to do operations on files of text type 
the operations are : 

the union function is used to check the existing of a word in two trees and insert it in a third one 

the intersection function is used to check the existing of a word in both of the trees and insert it in a third one 
    

when choosing the comparision way we can de define how we treat similar word or equals 
    for example 
    -regard and regarder will treated as the same if the user choose similarity based comparision
    -otherwise they would be treated as completely different 

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operation selected procedure is the menu procedure i made it not rewrite the code again and again 
since there is a repetation between the three operation union intersection and difference