\begin{thebibliography}{}+− +− \bibitem[Dyckhoff, 1992]{Dyckhoff92}+− Dyckhoff, R.+− \newblock {C}ontraction-{F}ree {S}equent {C}alculi for {I}ntuitionistic+− {L}ogic.+− \newblock {\em Journal of Symbolic Logic}, 57(3):795--807.+− +− \end{thebibliography}+−