diff --git a/assets/rbf_unit_sphere.svg b/assets/rbf_unit_sphere.svg
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diff --git a/index.md b/index.md
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@@ -45,4 +45,8 @@ Please cite our work if you find it useful:
Given a base kernel \\(\kappa\\), we define the kernel in the input-gradient space for a minibatch of training samples \\(\mathcal{B}=\\{(\mathbf{x}\_b, y\_b\\}\_{b=1}^B\\) as follows:
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+
+We choose the RBF kernel on a unit sphere as the base kernel \\(\kappa\\):
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+
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