diff --git a/CMakeLists.txt b/CMakeLists.txt
index 28f362ee..9cd2f3b3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -626,7 +626,7 @@ add_flex_bison_dependency(SdfLex SdfParser)
 include(FindSWIG)
 
 add_custom_command(OUTPUT ${STA_HOME}/app/StaApp_wrap.cc
-  COMMAND ${SWIG_EXECUTABLE} -tcl8 -c++ -namespace -prefix sta -o ${STA_HOME}/app/StaApp_wrap.cc ${STA_HOME}/app/StaApp.i
+  COMMAND ${SWIG_EXECUTABLE} -tcl8 -c++ -namespace -prefix sta -I${STA_HOME}/tcl -I${STA_HOME}/sdf -I${STA_HOME}/dcalc -I${STA_HOME}/parasitics -I${STA_HOME}/verilog -o ${STA_HOME}/app/StaApp_wrap.cc ${STA_HOME}/app/StaApp.i
   COMMAND ${STA_HOME}/etc/SwigCleanup.tcl ${STA_HOME}/app/StaApp_wrap.cc
   WORKING_DIRECTORY ${STA_HOME}
   DEPENDS ${STA_SWIG_FILES}
diff --git a/app/StaApp.i b/app/StaApp.i
index 68f32cd7..f38c4697 100644
--- a/app/StaApp.i
+++ b/app/StaApp.i
@@ -16,10 +16,10 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-%include "../tcl/StaException.i"
-%include "../tcl/StaTcl.i"
-%include "../verilog/Verilog.i"
-%include "../tcl/NetworkEdit.i"
-%include "../sdf/Sdf.i"
-%include "../dcalc/DelayCalc.i"
-%include "../parasitics/Parasitics.i"
+%include "StaException.i"
+%include "StaTcl.i"
+%include "Verilog.i"
+%include "NetworkEdit.i"
+%include "Sdf.i"
+%include "DelayCalc.i"
+%include "Parasitics.i"
diff --git a/liberty/EquivCells.cc b/liberty/EquivCells.cc
index e11caffa..b7cfc107 100644
--- a/liberty/EquivCells.cc
+++ b/liberty/EquivCells.cc
@@ -15,6 +15,7 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 #include "Machine.hh"
+#include "UnorderedMap.hh"
 #include "PortDirection.hh"
 #include "Transition.hh"
 #include "MinMax.hh"
@@ -28,14 +29,16 @@
 
 namespace sta {
 
-typedef Map<unsigned,LibertyCellSeq*, std::less<unsigned> > LibertyCellHashMap;
+typedef UnorderedMap<unsigned, LibertyCellSeq*> LibertyCellHashMap;
 typedef Set<LibertyCellSeq*> LibertyCellSeqSet;
 
 static LibertyCellEquivMap *
 findEquivCells1(const LibertyLibrary *library);
 static void
+deleteEquivCellMap(LibertyCellEquivMap *equiv_map);
+static void
 sortCellEquivs(LibertyCellEquivMap *cell_equivs);
-float
+static float
 cellDriveResistance(const LibertyCell *cell);
 
 static unsigned
@@ -55,15 +58,19 @@ static bool
 equivCellSequentials(const LibertyCell *cell1,
 		     const LibertyCell *cell2);
 
-LibertyCellEquivMap *
-makeEquivCellMap(const LibertyLibrary *library)
+void
+findEquivCells(const LibertyLibrary *library)
 {
+  // Build a map from each cell in the library to a group (CellSeq) of
+  // cells with equivalent functionality.
   LibertyCellEquivMap *cell_equivs = findEquivCells1(library);
+  // Sort by drive strength.
   sortCellEquivs(cell_equivs);
-  return cell_equivs;
+  deleteEquivCellMap(cell_equivs);
 }
 
-void
+// Delete the LibertyCellEquivMap returned by makeEquivCellMap.
+static void
 deleteEquivCellMap(LibertyCellEquivMap *equiv_map)
 {
   // Multiple cells can point to the same cell sequence, so collect
@@ -147,14 +154,21 @@ sortCellEquivs(LibertyCellEquivMap *cell_equivs)
   while (equivs_iter.hasNext()) {
     LibertyCellSeq *equivs = equivs_iter.next();
     sort(equivs, CellDriveResistanceLess());
+    LibertyCell *lower = nullptr;
+    LibertyCellSeq::Iterator cell_iter(equivs);
+    while (cell_iter.hasNext()) {
+      LibertyCell *cell = cell_iter.next();
+      if (lower) {
+	lower->setHigherDrive(cell);
+	cell->setLowerDrive(lower);
+      }
+      lower = cell;
+    }
   }
 }
 
 // Use the worst "drive" for all the timing arcs in the cell.
-// Note that this function can NOT be static for sun's compiler to
-// be happy with using it in a sort predicate (presumably because the
-// template functions are compiled outside the scope of this file).
-float
+static float
 cellDriveResistance(const LibertyCell *cell)
 {
   float max_drive = 0.0;
diff --git a/liberty/EquivCells.hh b/liberty/EquivCells.hh
index 63aa5ea9..2b831052 100644
--- a/liberty/EquivCells.hh
+++ b/liberty/EquivCells.hh
@@ -22,14 +22,10 @@
 
 namespace sta {
 
-// Build a map from each cell in the library to a group (CellSeq) of
-// cells with equivalent functionality, sorted by drive strength.
-LibertyCellEquivMap *
-makeEquivCellMap(const LibertyLibrary *library);
-
-// Delete the LibertyCellEquivMap returned by makeEquivCellMap.
+// Find equivalent cells, sort by drive strength and
+// and set cell->higherDrive/lowerDrive.
 void
-deleteEquivCellMap(LibertyCellEquivMap *equiv_map);
+findEquivCells(const LibertyLibrary *library);
 
 // Predicate that is true when the ports, functions, sequentials and
 // timing arcs match.
diff --git a/liberty/Liberty.cc b/liberty/Liberty.cc
index 5a267ba8..8f474a72 100644
--- a/liberty/Liberty.cc
+++ b/liberty/Liberty.cc
@@ -82,7 +82,6 @@ LibertyLibrary::LibertyLibrary(const char *name,
   default_wire_load_mode_(WireloadMode::unknown),
   default_wire_load_selection_(nullptr),
   default_operating_conditions_(nullptr),
-  equiv_cell_map_(nullptr),
   ocv_arc_depth_(0.0),
   default_ocv_derate_(nullptr)
 {
@@ -123,8 +122,6 @@ LibertyLibrary::~LibertyLibrary()
   operating_conditions_.deleteContents();
   wireloads_.deleteContents();
   wire_load_selections_.deleteContents();
-  if (equiv_cell_map_)
-    deleteEquivCellMap(equiv_cell_map_);
   delete units_;
   ocv_derate_map_.deleteContents();
 
@@ -500,15 +497,6 @@ LibertyLibrary::setDefaultOutputPinRes(const TransRiseFall *tr,
   default_output_pin_res_.setValue(tr, value);
 }
 
-LibertyCellSeq *
-LibertyLibrary::findEquivCells(LibertyCell *cell)
-{
-  if (equiv_cell_map_ == nullptr)
-    equiv_cell_map_ = makeEquivCellMap(this);
-  LibertyCellSeq *equivs = equiv_cell_map_->findKey(cell);
-  return equivs;
-}
-
 void
 LibertyLibrary::addWireload(Wireload *wireload)
 {
@@ -748,6 +736,12 @@ LibertyLibrary::makeCornerMap(LibertyCell *cell1,
   }
 }
 
+void
+LibertyLibrary::finish()
+{
+  findEquivCells(this);
+}
+
 ////////////////////////////////////////////////////////////////
 
 float
@@ -849,7 +843,9 @@ LibertyCell::LibertyCell(LibertyLibrary *library,
   ocv_derate_(nullptr),
   is_disabled_constraint_(false),
   leakage_power_(0.0),
-  leakage_power_exists_(false)
+  leakage_power_exists_(false),
+  higher_drive_(nullptr),
+  lower_drive_(nullptr)
 {
 }
 
@@ -1388,6 +1384,20 @@ LibertyCell::setCornerCell(LibertyCell *corner_cell,
 
 ////////////////////////////////////////////////////////////////
 
+void
+LibertyCell::setHigherDrive(LibertyCell *cell)
+{
+  higher_drive_ = cell;
+}
+
+void
+LibertyCell::setLowerDrive(LibertyCell *cell)
+{
+  lower_drive_ = cell;
+}
+
+////////////////////////////////////////////////////////////////
+
 float
 LibertyCell::ocvArcDepth() const
 {
diff --git a/liberty/Liberty.hh b/liberty/Liberty.hh
index fb603ecc..a0620e49 100644
--- a/liberty/Liberty.hh
+++ b/liberty/Liberty.hh
@@ -223,7 +223,6 @@ public:
   float slewDerateFromLibrary() const;
   void setSlewDerateFromLibrary(float derate);
 
-  LibertyCellSeq *findEquivCells(LibertyCell *cell);
   Units *units() { return units_; }
   const Units *units() const { return units_; }
 
@@ -279,6 +278,7 @@ public:
 		bool link,
 		int ap_index,
 		Report *report);
+  void finish();
 
 protected:
   float degradeWireSlew(const LibertyCell *cell,
@@ -322,7 +322,6 @@ protected:
   WireloadSelectionMap wire_load_selections_;
   OperatingConditionsMap operating_conditions_;
   OperatingConditions *default_operating_conditions_;
-  LibertyCellEquivMap *equiv_cell_map_;
   float ocv_arc_depth_;
   OcvDerate *default_ocv_derate_;
   OcvDerateMap ocv_derate_map_;
@@ -391,9 +390,6 @@ public:
   void setScaleFactors(ScaleFactors *scale_factors);
   ModeDef *makeModeDef(const char *name);
   ModeDef *findModeDef(const char *name);
-  // Add scaled cell after it is complete.
-  void addScaledCell(OperatingConditions *op_cond,
-		     LibertyCell *scaled_cell);
 
   float area() const { return area_; }
   void setArea(float area);
@@ -410,15 +406,6 @@ public:
   bool isClockGateOther() const;
   bool isClockGate() const;
   void setClockGateType(ClockGateType type);
-  virtual unsigned addTimingArcSet(TimingArcSet *set);
-  void addTimingArcAttrs(TimingArcAttrs *attrs);
-  virtual void addInternalPower(InternalPower *power);
-  void addInternalPowerAttrs(InternalPowerAttrs *attrs);
-  virtual void addLeakagePower(LeakagePower *power);
-  // Call after cell is finished being constructed.
-  virtual void finish(bool infer_latches,
-		      Report *report,
-		      Debug *debug);
   // Internal to LibertyCellTimingArcSetIterator.
   TimingArcSetSeq *timingArcSets(const LibertyPort *from,
 				 const LibertyPort *to) const;
@@ -427,13 +414,44 @@ public:
   TimingArcSet *findTimingArcSet(TimingArcSet *key) const;
   TimingArcSet *findTimingArcSet(unsigned arc_set_index) const;
   bool hasTimingArcs(LibertyPort *port) const;
+
   InternalPowerSeq *internalPowers() { return &internal_powers_; }
   LeakagePowerSeq *leakagePowers() { return &leakage_powers_; }
   void leakagePower(// Return values.
 		    float &leakage,
 		    bool &exists) const;
   bool leakagePowerEx() const { return leakage_power_exists_; }
+
   bool hasSequentials() const;
+  // Find the sequential with the output connected to an (internal) port.
+  Sequential *outputPortSequential(LibertyPort *port);
+
+  // Find bus declaration local to this cell.
+  BusDcl *findBusDcl(const char *name) const;
+  // True when TimingArcSetBuilder::makeRegLatchArcs infers register
+  // timing arcs.
+  bool hasInferedRegTimingArcs() const { return has_infered_reg_timing_arcs_; }
+  TestCell *testCell() const { return test_cell_; }
+  bool isLatchData(LibertyPort *port);
+  void latchEnable(TimingArcSet *arc_set,
+		   // Return values.
+		   LibertyPort *&enable_port,
+		   FuncExpr *&enable_func,
+		   TransRiseFall *&enable_tr) const;
+  TransRiseFall *latchCheckEnableTrans(TimingArcSet *check_set);
+  bool isDisabledConstraint() const { return is_disabled_constraint_; }
+  LibertyCell *cornerCell(int ap_index);
+
+  // AOCV
+  float ocvArcDepth() const;
+  OcvDerate *ocvDerate() const;
+  OcvDerate *findOcvDerate(const char *derate_name);
+
+  // Next higher/lower drive equivalent cells.
+  LibertyCell *higherDrive() const { return higher_drive_; }
+  LibertyCell *lowerDrive() const { return lower_drive_; }
+
+  // Build helpers.
   void makeSequential(int size,
 		      bool is_register,
 		      FuncExpr *clk,
@@ -444,40 +462,31 @@ public:
 		      LogicValue clr_preset_out_inv,
 		      LibertyPort *output,
 		      LibertyPort *output_inv);
-  // Find the sequential with the output connected to an (internal) port.
-  Sequential *outputPortSequential(LibertyPort *port);
-  // Find bus declaration local to this cell.
-  BusDcl *findBusDcl(const char *name) const;
   void addBusDcl(BusDcl *bus_dcl);
-  // True when TimingArcSetBuilder::makeRegLatchArcs infers register
-  // timing arcs.
-  bool hasInferedRegTimingArcs() const { return has_infered_reg_timing_arcs_; }
-  void setHasInferedRegTimingArcs(bool infered);
-  TestCell *testCell() const { return test_cell_; }
+  // Add scaled cell after it is complete.
+  void addScaledCell(OperatingConditions *op_cond,
+		     LibertyCell *scaled_cell);
+  virtual unsigned addTimingArcSet(TimingArcSet *set);
+  void addTimingArcAttrs(TimingArcAttrs *attrs);
+  virtual void addInternalPower(InternalPower *power);
+  void addInternalPowerAttrs(InternalPowerAttrs *attrs);
+  virtual void addLeakagePower(LeakagePower *power);
+  void setLeakagePower(float leakage);
+  void setOcvArcDepth(float depth);
+  void setOcvDerate(OcvDerate *derate);
+  void addOcvDerate(OcvDerate *derate);
+  void addPgPort(LibertyPgPort *pg_port);
   void setTestCell(TestCell *test);
-  bool isLatchData(LibertyPort *port);
-  void latchEnable(TimingArcSet *arc_set,
-		   // Return values.
-		   LibertyPort *&enable_port,
-		   FuncExpr *&enable_func,
-		   TransRiseFall *&enable_tr) const;
-  TransRiseFall *latchCheckEnableTrans(TimingArcSet *check_set);
-  bool isDisabledConstraint() const { return is_disabled_constraint_; }
+  void setHasInferedRegTimingArcs(bool infered);
   void setIsDisabledConstraint(bool is_disabled);
-  LibertyCell *cornerCell(int ap_index);
   void setCornerCell(LibertyCell *corner_cell,
 		     int ap_index);
-  void setLeakagePower(float leakage);
-
-  // AOCV
-  float ocvArcDepth() const;
-  void setOcvArcDepth(float depth);
-  OcvDerate *ocvDerate() const;
-  void setOcvDerate(OcvDerate *derate);
-  OcvDerate *findOcvDerate(const char *derate_name);
-  void addOcvDerate(OcvDerate *derate);
-
-  void addPgPort(LibertyPgPort *pg_port);
+  // Call after cell is finished being constructed.
+  virtual void finish(bool infer_latches,
+		      Report *report,
+		      Debug *debug);
+  void setHigherDrive(LibertyCell *cell);
+  void setLowerDrive(LibertyCell *cell);
 
 protected:
   virtual void addPort(ConcretePort *port);
@@ -511,7 +520,6 @@ protected:
   bool interface_timing_;
   ClockGateType clock_gate_type_;
   TimingArcSetSeq timing_arc_sets_;
-  // Used to find matching arc sets in equivalent cells.
   TimingArcSetMap timing_arc_set_map_;
   LibertyPortPairTimingArcMap port_timing_arc_set_map_;
   LibertyPortTimingArcMap timing_arc_set_from_map_;
@@ -542,6 +550,9 @@ protected:
   float leakage_power_;
   bool leakage_power_exists_;
   LibertyPgPortMap pg_port_map_;
+  // Next higher/lower drive equivalent cells.
+  LibertyCell *higher_drive_;
+  LibertyCell *lower_drive_;
 
 private:
   DISALLOW_COPY_AND_ASSIGN(LibertyCell);
diff --git a/liberty/LibertyReader.cc b/liberty/LibertyReader.cc
index 67550600..90a90f1f 100644
--- a/liberty/LibertyReader.cc
+++ b/liberty/LibertyReader.cc
@@ -578,6 +578,7 @@ void
 LibertyReader::endLibrary(LibertyGroup *group)
 {
   endLibraryAttrs(group);
+  library_->finish();
 }
 
 void
diff --git a/search/Property.cc b/search/Property.cc
index dee21fb7..14ca66ee 100644
--- a/search/Property.cc
+++ b/search/Property.cc
@@ -509,6 +509,10 @@ getProperty(const LibertyCell *cell,
     return PropertyValue(cell->filename());
   else if (stringEqual(property, "library"))
     return PropertyValue(cell->libertyLibrary());
+  else if (stringEqual(property, "higher_drive"))
+    return PropertyValue(cell->higherDrive());
+  else if (stringEqual(property, "lower_drive"))
+    return PropertyValue(cell->lowerDrive());
   else
     throw PropertyUnknown("liberty cell", property);
 }
@@ -706,7 +710,7 @@ pinSlewProperty(const Pin *pin,
 		const MinMax *min_max,
 		Sta *sta)
 {
-  auto graph = sta->graph();
+  auto graph = sta->ensureGraph();
   Vertex *vertex, *bidirect_drvr_vertex;
   graph->pinVertices(pin, vertex, bidirect_drvr_vertex);
   Slew slew = min_max->initValue();
diff --git a/search/Sta.cc b/search/Sta.cc
index 381b92ad..017e6af9 100644
--- a/search/Sta.cc
+++ b/search/Sta.cc
@@ -3214,7 +3214,7 @@ Sta::setArcDelay(Edge *edge,
 		 TimingArc *arc,
 		 const Corner *corner,
 		 const MinMaxAll *min_max,
-		 float delay)
+		 ArcDelay delay)
 {
   MinMaxIterator mm_iter(min_max);
   while (mm_iter.hasNext()) {
diff --git a/search/Sta.hh b/search/Sta.hh
index 95df50be..d5093cc2 100644
--- a/search/Sta.hh
+++ b/search/Sta.hh
@@ -705,7 +705,7 @@ public:
 		   TimingArc *arc,
 		   const Corner *corner,
 		   const MinMaxAll *min_max,
-		   float delay);
+		   ArcDelay delay);
   // Set annotated slew on a vertex for delay calculation.
   void setAnnotatedSlew(Vertex *vertex,
 			const Corner *corner,
diff --git a/tcl/StaTcl.i b/tcl/StaTcl.i
index 42ad15f7..3737886e 100644
--- a/tcl/StaTcl.i
+++ b/tcl/StaTcl.i
@@ -2275,13 +2275,6 @@ cells_equiv_ports(LibertyCell *cell1,
   return equivCellPorts(cell1, cell2);
 }
 
-LibertyCellSeq *
-find_equiv_cells(LibertyCell *cell)
-{
-  LibertyLibrary *library = cell->libertyLibrary();
-  return library->findEquivCells(cell);
-}
-
 void
 set_cmd_namespace_cmd(const char *namespc)
 {
@@ -2652,6 +2645,7 @@ PropertyValue
 pin_property(const Pin *pin,
 	     const char *property)
 {
+  cmdLinkedNetwork();
   return getProperty(pin, property, Sta::sta());
 }
 
@@ -2659,6 +2653,7 @@ PropertyValue
 instance_property(const Instance *inst,
 		  const char *property)
 {
+  cmdLinkedNetwork();
   return getProperty(inst, property, Sta::sta());
 }
 
@@ -2666,6 +2661,7 @@ PropertyValue
 net_property(const Net *net,
 	     const char *property)
 {
+  cmdLinkedNetwork();
   return getProperty(net, property, Sta::sta());
 }