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It must return a list of the items: value and messages
value 1 if there were model changes done in this procedure, 0 else.
If it returns -cancel- as a special value, then the transformation messages won't be shown.
file: the name of the model to be transformed;
oldproblemtype: the name of the previous problem type;
newproblemtype: the name of the problem type to be transformed.
messages: explains the transforming operations done.
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