Negative translations have been introduced to show the equi-consistency
of intuitionistic and classical logics. Since then, they have been
generalized and used in several different contexts. In this talk a
technique, inspired in the negative translation mechanism, to prove
that Craig interpolation holds in a deductive system is presented. This
technique is used to show that Craig interpolation is preserved by the
fibring of deductive systems under mild requirements. Other
preservation by fibring results are presented concerning the extension
interpolation property and the Maehara interpolation property. This
talk reports on joint work with Walter Carnielli and Cristina Sernadas.
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