Adding switch to enable reuse of proof-obligations in the last timeframe.

src/proof/pdr/pdr.h

@@ -52,6 +52,7 @@ struct Pdr_Par_t_
     int fMonoCnf;         // monolythic CNF
     int fDumpInv;         // dump inductive invariant
     int fShortest;        // forces bug traces to be shortest
+    int fReuseProofOblig; // reuses proof-obligationgs in the last timeframe
     int fSkipGeneral;     // skips expensive generalization step
     int fVerbose;         // verbose output`
     int fVeryVerbose;     // very verbose output

src/proof/pdr/pdrCore.c

@@ -525,7 +525,7 @@ int Pdr_ManBlockCube( Pdr_Man_t * p, Pdr_Set_t * pCube )
             for ( i = 1; i <= k; i++ )
                 Pdr_ManSolverAddClause( p, i, pCubeMin );
             // schedule proof obligation
-            if ( !p->pPars->fShortest )
+            if ( (k < kMax || p->pPars->fReuseProofOblig) && !p->pPars->fShortest )
             {
                 pThis->iFrame = k+1;
                 pThis->prio   = Prio--;