diff --git a/CMakeLists.txt b/CMakeLists.txt
index af438059..8f713ec5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -256,7 +256,7 @@ flex_target(LibertyLex ${STA_HOME}/liberty/LibertyLex.ll ${CMAKE_CURRENT_BINARY_
   COMPILE_FLAGS --prefix=LibertyLex_
   )
 bison_target(LibertyParser ${STA_HOME}/liberty/LibertyParse.yy ${CMAKE_CURRENT_BINARY_DIR}/LibertyParse.cc
-  COMPILE_FLAGS --name-prefix=LibertyParse_
+  COMPILE_FLAGS "--name-prefix=LibertyParse_ -v"
   )
 add_flex_bison_dependency(LibertyLex LibertyParser)
 
diff --git a/liberty/LibertyParse.yy b/liberty/LibertyParse.yy
index 2ac53a9d..e4177ae5 100644
--- a/liberty/LibertyParse.yy
+++ b/liberty/LibertyParse.yy
@@ -14,7 +14,7 @@
 // 
 // 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 <stdlib.h>
 #include <string.h>
 
@@ -26,27 +26,35 @@ int LibertyLex_lex();
 // Use yacc generated parser errors.
 #define YYERROR_VERBOSE
 
+#define YYDEBUG 1
+
 %}
 
 %union {
   char *string;
   float number;
   int line;
+  char ch;
   sta::LibertyAttrValue *attr_value;
   sta::LibertyAttrValueSeq *attr_values;
   sta::LibertyGroup *group;
   sta::LibertyStmt *stmt;
 }
 
+%left '+' '|'
+%left '*' '&'
+%left '^'
+%left '!'
+
 %token <number> FLOAT
 %token <string> STRING KEYWORD
 
 %type <stmt> statement complex_attr simple_attr variable group file
 %type <attr_values> attr_values
-%type <attr_value> attr_value simple_attr_value
-%type <string> string
+%type <attr_value> attr_value
+%type <string> string expr expr_term expr_term1 volt_expr
 %type <line> line
-%type <number> volt_expr volt_token
+%type <ch> expr_op volt_op
 
 %start file
 
@@ -61,11 +69,11 @@ file:
 
 group:
 	KEYWORD '(' ')' line '{'
-	{ sta::libertyGroupBegin($1, NULL, $4); }
+	{ sta::libertyGroupBegin($1, nullptr, $4); }
 	'}' semi_opt
 	{ $$ = sta::libertyGroupEnd(); }
 |	KEYWORD '(' ')' line '{'
-	{ sta::libertyGroupBegin($1, NULL, $4); }
+	{ sta::libertyGroupBegin($1, nullptr, $4); }
 	statements '}' semi_opt
 	{ $$ = sta::libertyGroupEnd(); }
 |	KEYWORD '(' attr_values ')' line '{'
@@ -95,23 +103,13 @@ statement:
 	;
 
 simple_attr:
-	KEYWORD ':' simple_attr_value line semi_opt
+	KEYWORD ':' attr_value line semi_opt
 	{ $$ = sta::makeLibertySimpleAttr($1, $3, $4); }
 	;
 
-simple_attr_value:
-	attr_value
-|	volt_expr
-	{ $$ = static_cast<sta::LibertyAttrValue*>(NULL); }
-/* Unquoted NOT function. */
-/* clocked_on : !CP; */
-|	'!' string
-	{ $$ = sta::makeLibertyStringAttrValue(sta::stringPrint("!%s", $2)); sta::stringDelete($2); }
-	;
-
 complex_attr:
 	KEYWORD '(' ')' line semi_opt
-	{ $$ = sta::makeLibertyComplexAttr($1, NULL, $4); }
+	{ $$ = sta::makeLibertyComplexAttr($1, nullptr, $4); }
 |	KEYWORD '(' attr_values ')' line semi_opt
 	{ $$ = sta::makeLibertyComplexAttr($1, $3, $5); }
 	;
@@ -146,29 +144,86 @@ string:
 attr_value:
 	FLOAT
 	{ $$ = sta::makeLibertyFloatAttrValue($1); }
-	| string
+|       expr
+	{ $$ = sta::makeLibertyStringAttrValue($1); }
+|	volt_expr
 	{ $$ = sta::makeLibertyStringAttrValue($1); }
 	;
 
 /* Voltage expressions are ignored. */
+/* Crafted to avoid conflicts with expr */
 volt_expr:
-	volt_token expr_op volt_token
-|	volt_expr expr_op volt_token
+        FLOAT volt_op FLOAT
+	{ $$ = sta::stringPrint("%e%c%e", $1, $2, $3); }
+|       string volt_op FLOAT
+	{ $$ = sta::stringPrint("%s%c%e", $1, $2, $3);
+          sta::stringDelete($1);
+        }
+|       FLOAT volt_op string
+	{ $$ = sta::stringPrint("%e%c%s", $1, $2, $3);
+          sta::stringDelete($3);
+        }
+|       volt_expr volt_op FLOAT
+	{ $$ = sta::stringPrint("%s%c%e", $1, $2, $3);
+          sta::stringDelete($1);
+        }
+        ;
+
+volt_op:
+	'+'
+        { $$ = '+'; }
+|	'-'
+        { $$ = '-'; }
+|	'*'
+        { $$ = '*'; }
+|	'/'
+        { $$ = '/'; }
 	;
 
-volt_token:
-	FLOAT
-|	KEYWORD
-	{ sta::stringDelete($1);
-	  $$ = 0.0;
-	}
+expr:
+        expr_term1
+|	expr_term1 expr_op expr
+	{ $$ = sta::stringPrint("%s%c%s", $1, $2, $3);
+          sta::stringDelete($1);
+          sta::stringDelete($3);
+        }
+	;
+
+expr_term:
+	string
+|	'0'
+	{ $$ = sta::stringPrint("0"); }
+|	'1'
+	{ $$ = sta::stringPrint("1"); }
+|	'(' expr ')'
+	{ $$ = sta::stringPrint("(%s)", $2);
+          sta::stringDelete($2);
+        }
+	;
+
+expr_term1:
+	expr_term
+|       '!' expr_term
+	{ $$ = sta::stringPrint("!%s", $2);
+          sta::stringDelete($2);
+        }
+|	expr_term '\''
+	{ $$ = sta::stringPrint("%s'", $1);
+          sta::stringDelete($1);
+        }
 	;
 
 expr_op:
 	'+'
-|	'-'
+        { $$ = '+'; }
+|	'|'
+        { $$ = '|'; }
 |	'*'
-|	'/'
+        { $$ = '*'; }
+|	'&'
+        { $$ = '&'; }
+|	'^'
+        { $$ = '^'; }
 	;
 
 semi_opt:
diff --git a/liberty/LibertyReader.cc b/liberty/LibertyReader.cc
index 42d94c04..85cc353f 100644
--- a/liberty/LibertyReader.cc
+++ b/liberty/LibertyReader.cc
@@ -40,6 +40,8 @@
 #include "ParseBus.hh"
 #include "Network.hh"
 
+extern int LibertyParse_debug;
+
 namespace sta {
 
 static void
@@ -138,6 +140,7 @@ LibertyReader::readLibertyFile(const char *filename,
     have_slew_upper_threshold_[rf_index] = false;
   }
 
+  //::LibertyParse_debug = 1;
   parseLibertyFile(filename, this, report_);
   return library_;
 }