diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
index 294b6ba..554e958 100644
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,7 +1,10 @@
 0.2.0.0
 -------
-* allow parsing maximization problem as specified in
+* Support some features described in “General OPB Format”
   https://www.cril.univ-artois.fr/PB24/OPBgeneral.pdf
+  * allow both min and max keywords in the objective function
+  * allow any usual relational operator in constraints
+  * allow to use Unicode characters and the UTF-8 encoding for relational operators
 
 0.1.11.0
 -------
diff --git a/pseudo-boolean.cabal b/pseudo-boolean.cabal
index 6088237..90d04b0 100644
--- a/pseudo-boolean.cabal
+++ b/pseudo-boolean.cabal
@@ -67,7 +67,9 @@ library
      deepseq >=1.4.4.0,
      hashable >=1.2.7.0 && <1.5.0.0,
      void,
-     OptDir >= 0.1.0
+     OptDir >= 0.1.0,
+     utf8-string >=1.0.1.1 && <1.1,
+     text >=1.2.3.1 && <3.0
   hs-source-dirs:      src
   default-language:    Haskell2010
 
diff --git a/src/Data/PseudoBoolean/Attoparsec.hs b/src/Data/PseudoBoolean/Attoparsec.hs
index 6da8436..479f422 100644
--- a/src/Data/PseudoBoolean/Attoparsec.hs
+++ b/src/Data/PseudoBoolean/Attoparsec.hs
@@ -39,6 +39,7 @@ import Data.Attoparsec.ByteString.Char8 hiding (isDigit)
 import qualified Data.Attoparsec.ByteString.Lazy as L
 import qualified Data.ByteString.Char8 as BS
 import qualified Data.ByteString.Lazy as BSLazy
+import qualified Data.ByteString.UTF8 as UTF8
 import Data.Char
 import Data.Maybe
 import Data.PseudoBoolean.Types
@@ -157,7 +158,19 @@ objective_type = (string "min:" >> return OptMin) <|> (string "max:" >> return O
 
 -- <relational_operator>::= ">=" | "="
 relational_operator :: Parser Op
-relational_operator = (string ">=" >> return Ge) <|> (string "=" >> return Eq)
+relational_operator = msum
+  [ string "=" >> return Eq
+  , string "!=" >> return NEq
+  , string ">=" >> return Ge
+  , string ">" >> return Gt
+  , string "<=" >> return Le
+  , string "<" >> return Lt
+  , u8string "≠" >> return NEq
+  , u8string "≥" >> return Ge
+  , u8string "≤" >> return Le
+  ]
+  where
+    u8string = string . UTF8.fromString
 
 -- <variablename>::= "x" <unsigned_integer>
 variablename :: Parser Var
diff --git a/src/Data/PseudoBoolean/Builder.hs b/src/Data/PseudoBoolean/Builder.hs
index f51f261..a1cf104 100644
--- a/src/Data/PseudoBoolean/Builder.hs
+++ b/src/Data/PseudoBoolean/Builder.hs
@@ -99,7 +99,11 @@ showConstraint (lhs, op, rhs) =
   showSum lhs <> f op <>  fromString " " <> fromString (show rhs) <> fromString ";\n"
   where
     f Eq = fromString "="
+    f NEq = fromString "!="
+    f Gt = fromString ">"
     f Ge = fromString ">="
+    f Lt = fromString "<"
+    f Le = fromString "<="
 
 showSoftConstraint :: (Monoid a, IsString a) => SoftConstraint -> a
 showSoftConstraint (cost, constr) =
diff --git a/src/Data/PseudoBoolean/ByteStringBuilder.hs b/src/Data/PseudoBoolean/ByteStringBuilder.hs
index 91f556e..efdacf1 100644
--- a/src/Data/PseudoBoolean/ByteStringBuilder.hs
+++ b/src/Data/PseudoBoolean/ByteStringBuilder.hs
@@ -107,7 +107,11 @@ showConstraint (lhs, op, rhs) =
   showSum lhs <> f op <>  char7 ' ' <> integerDec rhs <> string7 ";\n"
   where
     f Eq = char7 '='
+    f NEq = string7 "!="
+    f Gt = string7 ">"
     f Ge = string7 ">="
+    f Lt = string7 "<"
+    f Le = string7 "<="
 
 showSoftConstraint :: SoftConstraint -> Builder
 showSoftConstraint (cost, constr) =
diff --git a/src/Data/PseudoBoolean/Megaparsec.hs b/src/Data/PseudoBoolean/Megaparsec.hs
index b4e52e8..0a72451 100644
--- a/src/Data/PseudoBoolean/Megaparsec.hs
+++ b/src/Data/PseudoBoolean/Megaparsec.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE BangPatterns, FlexibleContexts, TypeFamilies, ConstraintKinds #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeOperators #-}
 {-# OPTIONS_GHC -Wall #-}
 -----------------------------------------------------------------------------
@@ -42,8 +43,10 @@ module Data.PseudoBoolean.Megaparsec
 import Prelude hiding (sum)
 import Control.Monad
 import Data.ByteString.Lazy (ByteString)
-import qualified Data.ByteString.Lazy.Char8 as BL
+import qualified Data.ByteString.Lazy as BL
+import qualified Data.ByteString.Lazy.UTF8 as UTF8
 import Data.Maybe
+import Data.Proxy
 import Data.String
 import Data.Word
 import Data.Void
@@ -173,8 +176,21 @@ objective_type :: C e s m => m OptDir
 objective_type = (try (string "min:") >> return OptMin) <|> (string "max:" >> return OptMax)
 
 -- <relational_operator>::= ">=" | "="
-relational_operator :: C e s m => m Op
-relational_operator = (string ">=" >> return Ge) <|> (string "=" >> return Eq)
+relational_operator :: forall e s m. C e s m => m Op
+relational_operator = msum $ map try
+  [ string "=" >> return Eq
+  , string "!=" >> return NEq
+  , string ">=" >> return Ge
+  , string ">" >> return Gt
+  , string "<=" >> return Le
+  , string "<" >> return Lt
+  , u8string "≠" >> return NEq
+  , u8string "≥" >> return Ge
+  , u8string "≤" >> return Le
+  ]
+  where
+    -- XXX: We cannot assume Tokens s ~ ByteString
+    u8string s = label s (string . tokensToChunk (Proxy :: Proxy s) . BL.unpack  . UTF8.fromString $ s)
 
 -- <variablename>::= "x" <unsigned_integer>
 variablename :: C e s m => m Var
@@ -224,7 +240,7 @@ type ParseError = MP.ParseErrorBundle BL.ByteString Void
 
 -- | Parse a OPB format string containing pseudo boolean problem.
 parseOPBString :: String -> String -> Either ParseError Formula
-parseOPBString info s = parse (formula <* eof) info (BL.pack s)
+parseOPBString info s = parse (formula <* eof) info (UTF8.fromString s)
 
 -- | Parse a OPB format lazy bytestring containing pseudo boolean problem.
 parseOPBByteString :: String -> ByteString -> Either ParseError Formula
@@ -287,7 +303,7 @@ softconstraint = do
 
 -- | Parse a WBO format string containing weighted boolean optimization problem.
 parseWBOString :: String -> String -> Either ParseError SoftFormula
-parseWBOString info s = parse (softformula <* eof) info (BL.pack s)
+parseWBOString info s = parse (softformula <* eof) info (UTF8.fromString s)
 
 -- | Parse a WBO format lazy bytestring containing pseudo boolean problem.
 parseWBOByteString :: String -> ByteString -> Either ParseError SoftFormula
diff --git a/src/Data/PseudoBoolean/Parsec.hs b/src/Data/PseudoBoolean/Parsec.hs
index f2ab8e3..df9eb02 100644
--- a/src/Data/PseudoBoolean/Parsec.hs
+++ b/src/Data/PseudoBoolean/Parsec.hs
@@ -37,9 +37,10 @@ module Data.PseudoBoolean.Parsec
 import Prelude hiding (sum)
 import Control.Monad
 import Data.ByteString.Lazy (ByteString)
+import qualified Data.ByteString.Lazy as BL
 import Data.Maybe
+import qualified Data.Text.Lazy.Encoding as TL
 import Text.Parsec
-import qualified Text.Parsec.ByteString.Lazy as ParsecBS
 import Data.PseudoBoolean.Types
 import Data.PseudoBoolean.Internal.TextUtil
 
@@ -156,7 +157,17 @@ objective_type = (try (string "min:") >> return OptMin) <|> (string "max:" >> re
 
 -- <relational_operator>::= ">=" | "="
 relational_operator :: Stream s m Char => ParsecT s u m Op
-relational_operator = (string ">=" >> return Ge) <|> (string "=" >> return Eq)
+relational_operator = msum $ map try
+  [ string "=" >> return Eq
+  , string "!=" >> return NEq
+  , string ">=" >> return Ge
+  , string ">" >> return Gt
+  , string "<=" >> return Le
+  , string "<" >> return Lt
+  , string "≠" >> return NEq
+  , string "≥" >> return Ge
+  , string "≤" >> return Le
+  ]
 
 -- <variablename>::= "x" <unsigned_integer>
 variablename :: Stream s m Char => ParsecT s u m Var
@@ -215,7 +226,9 @@ parseOPBByteString = parse (formula <* eof)
 
 -- | Parse a OPB file containing pseudo boolean problem.
 parseOPBFile :: FilePath -> IO (Either ParseError Formula)
-parseOPBFile = ParsecBS.parseFromFile (formula <* eof)
+parseOPBFile fname = do
+  input <- BL.readFile fname
+  return $ runP (formula <* eof) () fname (TL.decodeUtf8 input)
 
 
 -- <softformula>::= <sequence_of_comments> <softheader> <sequence_of_comments_or_constraints>
@@ -277,4 +290,6 @@ parseWBOByteString = parse (softformula <* eof)
 
 -- | Parse a WBO file containing weighted boolean optimization problem.
 parseWBOFile :: FilePath -> IO (Either ParseError SoftFormula)
-parseWBOFile = ParsecBS.parseFromFile (softformula <* eof)
+parseWBOFile fname = do
+  input <- BL.readFile fname
+  return $ runP (softformula <* eof) () fname (TL.decodeUtf8 input)
diff --git a/src/Data/PseudoBoolean/Types.hs b/src/Data/PseudoBoolean/Types.hs
index 973b298..113d29b 100644
--- a/src/Data/PseudoBoolean/Types.hs
+++ b/src/Data/PseudoBoolean/Types.hs
@@ -75,7 +75,11 @@ type Constraint = (Sum, Op, Integer)
 -- | Relational operators
 data Op
   = Ge -- ^ /greater than or equal/
+  | Le -- ^ /lesser than or equal/
+  | Gt -- ^ /greater than/
+  | Lt -- ^ /lesser than/
   | Eq -- ^ /equal/
+  | NEq -- ^ /not equal/
   deriving (Eq, Ord, Show, Read, Enum, Bounded, Typeable, Data, Generic)
 
 instance NFData Op
diff --git a/test/TestPBFile.hs b/test/TestPBFile.hs
index ebb6dbf..4a64cea 100644
--- a/test/TestPBFile.hs
+++ b/test/TestPBFile.hs
@@ -48,6 +48,20 @@ case_invalid_lhs_empty_sum = checkOPBFile "test/samples/invalid-lhs-empty-sum.op
 case_invalid_lhs_empty_sum_wbo = checkWBOFile "test/samples/invalid-lhs-empty-sum.wbo"
 
 case_general_testlin_max_file  = checkOPBFile "test/samples/general/testlin-max.pb"
+case_general_relational_operator_file  = checkOPBFile "test/samples/general/test-relational-operator.pb"
+case_general_relational_operator_unicode_file  = checkOPBFile "test/samples/general/test-relational-operator-unicode.pb"
+case_general_relational_operator = checkOPBString "general relational operator" exampleGeneralRelationalOperator
+case_general_relational_operator_unicode = checkOPBString "general relational operator unicode" exampleGeneralRelationalOperatorUnicode
+
+case_general_relational_operator_unicode_equivalence = do
+  Right expected <- parseOPBFile "test/samples/general/test-relational-operator.pb"
+  Right opbP <- parseOPBFile "test/samples/general/test-relational-operator-unicode.pb"
+  expected @?= opbP
+  Right opbM <- M.parseOPBFile "test/samples/general/test-relational-operator-unicode.pb"
+  expected @?= opbM
+  Right opbA <- A.parseOPBFile "test/samples/general/test-relational-operator-unicode.pb"
+  expected @?= opbA
+
 
 case_trailing_junk = do
   isError (parseOPBString "" trailingJunk) @?= True
@@ -299,6 +313,30 @@ exampleWBO3 = unlines $
   , "-1 x3 -1 x4 >= -1 ;"
   ]
 
+exampleGeneralRelationalOperator :: String
+exampleGeneralRelationalOperator  = unlines $
+  [ "* #variable= 7 #constraint= 6"
+  , "max: 1 x1 ;"
+  , "+1 x1 +2 x2 >= 1;"
+  , "-1 x2 -2 x3 <= -1;"
+  , "+1 x3 +2 x4 > 1;"
+  , "-1 x4 -2 x5 < 0;"
+  , "+1 x5 +2 x6 = 3;"
+  , "-1 x6 -2 x7 != -3;"
+  ]
+
+exampleGeneralRelationalOperatorUnicode :: String
+exampleGeneralRelationalOperatorUnicode  = unlines $
+  [ "* #variable= 7 #constraint= 6"
+  , "max: 1 x1 ;"
+  , "+1 x1 +2 x2 ≥ 1;"
+  , "-1 x2 -2 x3 ≤ -1;"
+  , "+1 x3 +2 x4 > 1;"
+  , "-1 x4 -2 x5 < 0;"
+  , "+1 x5 +2 x6 = 3;"
+  , "-1 x6 -2 x7 ≠ -3;"
+  ]
+
 ------------------------------------------------------------------------
 -- Utilities
 
diff --git a/test/samples/general/test-relational-operator-unicode.pb b/test/samples/general/test-relational-operator-unicode.pb
new file mode 100644
index 0000000..442ab73
--- /dev/null
+++ b/test/samples/general/test-relational-operator-unicode.pb
@@ -0,0 +1,8 @@
+* #variable= 7 #constraint= 6
+max: 1 x1 ;
++1 x1 +2 x2 ≥ 1;
+-1 x2 -2 x3 ≤ -1;
++1 x3 +2 x4 > 1;
+-1 x4 -2 x5 < 0;
++1 x5 +2 x6 = 3;
+-1 x6 -2 x7 ≠ -3;
diff --git a/test/samples/general/test-relational-operator.pb b/test/samples/general/test-relational-operator.pb
new file mode 100644
index 0000000..ca3890f
--- /dev/null
+++ b/test/samples/general/test-relational-operator.pb
@@ -0,0 +1,8 @@
+* #variable= 7 #constraint= 6
+max: 1 x1 ;
++1 x1 +2 x2 >= 1;
+-1 x2 -2 x3 <= -1;
++1 x3 +2 x4 > 1;
+-1 x4 -2 x5 < 0;
++1 x5 +2 x6 = 3;
+-1 x6 -2 x7 != -3;