diff --git a/mtl/ast.py b/mtl/ast.py
index b73df21..736a9d1 100644
--- a/mtl/ast.py
+++ b/mtl/ast.py
@@ -103,7 +103,7 @@ class _Top(AST):
     __slots__ = ()
 
     def __repr__(self):
-        return "1"
+        return "TRUE"
 
     def __invert__(self):
         return BOT
@@ -113,7 +113,7 @@ class _Bot(AST):
     __slots__ = ()
 
     def __repr__(self):
-        return "0"
+        return "FALSE"
 
     def __invert__(self):
         return TOP
diff --git a/mtl/hypothesis.py b/mtl/hypothesis.py
index 07ebc35..07d378a 100644
--- a/mtl/hypothesis.py
+++ b/mtl/hypothesis.py
@@ -7,7 +7,7 @@ GRAMMAR = {
     'phi': (
         ('Unary', 'phi'),
         ('(', 'phi', 'Binary', 'phi', ')'),
-        ('AP', ), ('0', ), ('1', )
+        ('AP', ), ('FALSE', ), ('TRUE', )
     ),
     'Unary': (('~', ), ('G', 'Interval'), ('F', 'Interval'), ('X', )),
     'Interval': (('', ), ('[1, 3]', )),
diff --git a/mtl/parser.py b/mtl/parser.py
index eedb03a..e0d5dd9 100644
--- a/mtl/parser.py
+++ b/mtl/parser.py
@@ -40,8 +40,8 @@ const_or_unbound = const / "inf" / id
 
 AP = ~r"[a-z][a-z\d]*"
 
-bot = "False"
-top = "True"
+bot = "FALSE"
+top = "TRUE"
 
 id = ~r"[a-z\d]+"
 const = ~r"[-+]?(\d*\.\d+|\d+)"