Negation support for binary Enum

Enum.h

@@ -224,6 +224,15 @@ namespace Alepha::Hydrogen  ::detail::  Enum_m
 			}
 	};
 
+	template< EnumValueString no, EnumValueString yes >
+	constexpr Enum< no, yes >
+	operator not ( Enum< no, yes > enumeration )
+	{
+		enumeration.set_index( 1 - enumeration.get_index() );
+
+		return enumeration;
+	}
+
 	namespace exports
 	{
 		template< auto ... values >

Enum.test/0.cc

@@ -9,6 +9,16 @@ static_assert( __cplusplus > 2020'99 );
 
 #include <Alepha/IOStreams/String.h>
 
+namespace
+{
+	template< typename T >
+	concept CanNegate=
+	requires( const T &t )
+	{
+		{ not t };
+	};
+}
+
 static auto init= Alepha::Utility::enroll <=[]
 {
 	using namespace Alepha::literals::enum_literals;
@@ -58,4 +68,21 @@ static auto init= Alepha::Utility::enroll <=[]
 	{
 		{ "Wrong", { "Wrong" }, { "Adam", "Baker", "Charlie", "David" } },
 	};
+
+	static_assert( not CanNegate< Alepha::Enum< "one"_value > > );
+	static_assert(     CanNegate< Alepha::Enum< "one"_value, "two"_value > > );
+	static_assert( not CanNegate< Alepha::Enum< "one"_value, "two"_value, "three"_value > > );
+
+	"Does negation of a two form enum work?"_test <=TableTest
+	<
+		[]( const Alepha::Enum< "No"_value, "Yes"_value > e )
+		{
+			return not e;
+		}
+	>
+	::Cases
+	{
+		{ "No -> Yes", { "No"_value }, "Yes"_value },
+		{ "Yes -> No", { "Yes"_value }, "No"_value },
+	};
 };