@article{compref88,
   author = {Cohen,DE and Madlener,K and Otto,F},
   year = {1993},
   title = {Seperating the Intrinsic Complexity and the Derivational Complexity of the Word Problem for Finitely Presented Groups},
   journal = {Mathematical Logic Quarterly},
   volume = {39},
   pages = {143-157}
}

@book{compref132,
   author = {Girard,JY},
   year = {1987},
   title = {Proof Theory and Logical Complexity},
   publisher = {Bibliopolis},
   address = {Naples}
}