diff --git a/p_space_test.ipynb b/p_space_test.ipynb
index c1c79b1..6bdbcd0 100644
--- a/p_space_test.ipynb
+++ b/p_space_test.ipynb
@@ -29,6 +29,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "# ResonanceEC: Eq. (21)\n",
     "g1(α, p, q) = sqrt(α/(4*π))*((1/α+2/(p*q))*exp(-(p+q)^2/(4*α))+(1/α-2/(p*q))*exp(-(p-q)^2/(4*α)))\n",
     "V_pq(p, q) = -10 * g1(1, p, q)\n",
     "\n",