diff --git a/CGAL_Core/examples/Core/CMakeLists.txt b/CGAL_Core/examples/Core/CMakeLists.txt
index d4513e22dea4..6d9e732db932 100644
--- a/CGAL_Core/examples/Core/CMakeLists.txt
+++ b/CGAL_Core/examples/Core/CMakeLists.txt
@@ -9,4 +9,5 @@ if(NOT CGAL_Core_FOUND)
   return()
 endif()
 
+create_single_source_cgal_program("zero-one.cpp")
 create_single_source_cgal_program("delaunay.cpp")
diff --git a/CGAL_Core/examples/Core/zero-one.cpp b/CGAL_Core/examples/Core/zero-one.cpp
new file mode 100644
index 000000000000..cfc5a903c19b
--- /dev/null
+++ b/CGAL_Core/examples/Core/zero-one.cpp
@@ -0,0 +1,32 @@
+
+#include <CGAL/CORE_Expr.h>
+
+typedef CORE::Expr Real;
+
+int main()
+{
+  Real r(3.14);
+
+  CGAL::is_zero(r);
+
+  CGAL::is_one(r);
+
+  r = CGAL::sqrt(r);
+
+
+  CGAL::is_zero(r);
+
+  CGAL::is_one(r);
+
+  r = r * r;
+
+  CGAL::is_zero(r);
+
+  CGAL::is_one(r);
+
+  r = r - r;
+
+  CGAL::is_zero(r);
+
+  return 0;
+}
diff --git a/Number_types/include/CGAL/CORE_Expr.h b/Number_types/include/CGAL/CORE_Expr.h
index efeb5ad9363a..3ddb4c7f78fd 100644
--- a/Number_types/include/CGAL/CORE_Expr.h
+++ b/Number_types/include/CGAL/CORE_Expr.h
@@ -123,6 +123,22 @@ template <> class Algebraic_structure_traits< CORE::Expr >
         }
     };
 
+    class Is_one
+      : public CGAL::cpp98::unary_function< Type, bool > {
+      public:
+        bool operator()( const Type& x ) const {
+          double inf, sup;
+          x.doubleInterval(inf,sup);
+          if((inf > 1) || (sup < 1)){
+            return false;
+          }
+          if((inf == 1) && (sup == 1)){
+            return true;
+          }
+          return x.cmp(Type::getOne());
+        }
+    };
+
 };
 
 template <> class Real_embeddable_traits< CORE::Expr >