A unified approach to relative interpolation
Although Craig's interpolation theorem does not extend to infinitary languages in general, weaker forms are known to hold in special cases. One of these weakenings - relative interpolation - consists in allowing the interpolant to belong to a stronger language. Using a modified version of the model existence theorem the author develops a general method which yields all the hitherto known relative interpolation results.
scientific article; zbMATH DE number 4072937