diff --git a/doc/kernel_implementation.rst b/doc/kernel_implementation.rst
index 327c001e..57b37c8e 100644
--- a/doc/kernel_implementation.rst
+++ b/doc/kernel_implementation.rst
@@ -3,8 +3,15 @@
 List of implemented kernels
 ***************************
 
+The :math:`\checkmark` symbol represents the functions that have been implemented for each kernel.
+
+..  |tick|
+
+..  |tick| image:: tick.png
+
+
 ======  ===========  ===  ======= =========== =============== ======= =========== ====== ====== =======
  NAME     get/set    K    Kdiag   dK_dtheta   dKdiag_dtheta   dK_dX   dKdiag_dX   psi0   psi1   psi2
 ======  ===========  ===  ======= =========== =============== ======= =========== ====== ====== =======
-rbf     \\checkmark   y
+rbf     \\checkmark   y  
 ======  ===========  ===  ======= =========== =============== ======= =========== ====== ====== =======