From 85b7cc0d2303caee20fa33e7de316e0a60fe6506 Mon Sep 17 00:00:00 2001
From: Mathias Soeken <mathias.soeken@epfl.ch>
Date: Sat, 23 Jun 2018 08:23:30 -0700
Subject: [PATCH] Property function: is_symmetric_in.

---
 docs/changelog.rst           |  3 +++
 docs/properties.rst          |  1 +
 include/kitty/properties.hpp | 16 ++++++++++++++++
 3 files changed, 20 insertions(+)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 07246000..5e77ec02 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -13,6 +13,9 @@ v0.5 (not yet released)
 * Assignment operator for truth tables
   `#54 <https://github.com/msoeken/kitty/pull/54>`_
 
+* Function properties: ``is_symmetric_in``
+  `#55 <https://github.com/msoeken/kitty/pull/55>`_
+
 v0.4 (May 4, 2018)
 ------------------
 
diff --git a/docs/properties.rst b/docs/properties.rst
index bc8108ad..45814b43 100644
--- a/docs/properties.rst
+++ b/docs/properties.rst
@@ -9,3 +9,4 @@ properties.
    is_canalizing
    is_horn
    is_krom
+   is_symmetric_in
diff --git a/include/kitty/properties.hpp b/include/kitty/properties.hpp
index 74f5eef4..4049ca97 100644
--- a/include/kitty/properties.hpp
+++ b/include/kitty/properties.hpp
@@ -37,6 +37,8 @@
 #include <vector>
 
 #include "bit_operations.hpp"
+#include "operations.hpp"
+#include "operators.hpp"
 
 namespace kitty
 {
@@ -158,4 +160,18 @@ bool is_krom( const TT& tt )
   return true;
 }
 
+/*! \brief Checks whether a function is symmetric in a pair of variables
+
+  A function is symmetric in two variables, if it is invariant to swapping them.
+
+  \param tt Truth table
+  \param var_index1 Index of first variable
+  \param var_index2 Index of second variable
+*/
+template<typename TT>
+bool is_symmetric_in( const TT& tt, uint8_t var_index1, uint8_t var_index2 )
+{
+  return tt == swap( tt, var_index1, var_index2 );
+}
+
 } // namespace kitty