CERESω
Summary
is an extension of CERES to higher order logic. Please be sure to read the material on CERES before continuing. On this page,
we will focus on the description of the differences between
and
.
For details on
, please see Hetzl, Leitsch, Weller and Woltzenlogel Paleo 2009,
Weller 2010 and Hetzl, Leitsch and Weller 2011.
The system included in the generic architecture for proofs framework contains the implementation of the method, which at the moment provides the sequent calculus
and the characteristic sequent set computation for higher order proofs.
The method
The method proceeds analogously to the CERES method for first-order logic.
As input, the method takes a proof in a higher-order version of
, which
is the usual
with additional higher-order quantifier rules
![\begin{displaymath}
\infer[\foralllnt]{\forall\HT{R}, \Gamma \seq \Delta}{
\HT{R...
...\seq \Delta, \forall \HT{R}}
{\Gamma \seq \Delta,\HT{R}\HT{X}}
\end{displaymath}](omega-img5.png)
for all higher-order quantifiers, where





Such a proof is translated into a proof in the calculus (which is the step corresponding to
the Skolemization transformation in first-order CERES). This calculus operates on labelled sequents written
,
which are usual higher-order sequents where to every formula in the sequent, a multiset of terms called a label is associated.
is essentially
, where the eigenvariable condition is removed and instead, Skolem terms
are introduced. The arguments of the Skolem functions are tracked by the labels. This yields the quantifier rules
![\begin{displaymath}
\infer[\forallsklnt]{\ls{\forall_\alpha\HT{F}}{\ell}, \Gamma...
... \seq \Delta, \ls{\HT{F}(\SF{f}\HT{S}_1\ldots\HT{S}_n)}{\ell}}
\end{displaymath}](omega-img11.png)
where


From such an -proof
, a set of labelled sequents
,
the characteristic sequent set, can be extracted (which corresponds to the characteristic clause set of first-order CERES).
Finally, the
calculus
![\begin{displaymath}
\infer[\notT]{\ls{\HT{A}}{\ell},\Gamma\seq\Delta}{\Gamma\seq...
...ta,\ls{\HT{A}}{\ell}}{\ls{\neg \HT{A}}{\ell},\Gamma\seq\Delta}
\end{displaymath}](omega-img17.png)
![\begin{displaymath}
\infer[\orT]{\Gamma\seq\Delta,\ls{\HT{A}}{\ell}, \ls{\HT{B}}...
...Gamma\seq\Delta}{\ls{\HT{A}\vee\HT{B}}{\ell},\Gamma\seq\Delta}
\end{displaymath}](omega-img18.png)
![\begin{displaymath}
\infer[\allT]{\Gamma\seq\Delta, \ls{\HT{A}\HT{X}}{\ell,\HT{X...
...eq\Delta}
\qquad
\infer[\Sub]{S\subst{\HT{X}\goesto\HT{T}}}{S}
\end{displaymath}](omega-img19.png)
![\begin{displaymath}
\infer[\Cut]{\Gamma,\Pi\seq\Delta,\Lambda}{
\Gamma\seq\Delta...
...HT{A}}{\ell_{n+1}},\ldots,\ls{\HT{A}}{\ell_m},\Pi\seq\Lambda
}
\end{displaymath}](omega-img20.png)
is used to refute the characteristic sequent set. From such a refutation, a cut-free
