An SOS Message: Conservative Extension
                   in Higher-Order Positive/Negative 
                      Conditional Term Rewriting

                            Wan Fokkink
                           Chris Verhoef

 
General theorems in structured operational
semantics can be transformed into related results in conditional
term rewriting. We apply this approach to obtain
a conservative extension theorem
for higher-order conditional term rewriting
systems with negative conditions. This result is useful, for instance,
in modular specification of abstract data types, and in software
renovation factories.