1 files changed, 14 insertions, 21 deletions
diff --git a/source/know/concept/curvilinear-coordinates/index.md b/source/know/concept/curvilinear-coordinates/index.md
index cb22e43..48a5a72 100644
--- a/source/know/concept/curvilinear-coordinates/index.md
+++ b/source/know/concept/curvilinear-coordinates/index.md
@@ -48,6 +48,7 @@ we derive general formulae to convert expressions
 from Cartesian coordinates to the new orthogonal system $$(x_1, x_2, x_3)$$.
 
 
+
 ## Basis vectors
 
 Consider the the vector form of the line element $$\dd{\ell}$$,
@@ -86,6 +87,7 @@ $$\begin{aligned}
 \end{aligned}$$
 
 
+
 ## Gradient
 
 In an orthogonal coordinate system,
@@ -102,11 +104,8 @@ $$\begin{gathered}
     }
 \end{gathered}$$
 
-<div class="accordion">
-<input type="checkbox" id="proof-grad"/>
-<label for="proof-grad">Proof</label>
-<div class="hidden" markdown="1">
-<label for="proof-grad">Proof.</label>
+
+{% include proof/start.html id="proof-grad" -%}
 For a direction $$\dd{\ell}$$, we know that
 $$\idv{f}{\ell}$$ is the component of $$\nabla f$$ in that direction:
 
@@ -127,9 +126,8 @@ $$\begin{gathered}
     + \vu{e}_2 \dv{x_2}{\ell} \pdv{f}{x_2}
     + \vu{e}_3 \dv{x_3}{\ell} \pdv{f}{x_3}
 \end{gathered}$$
+{% include proof/end.html id="proof-grad" %}
 
-</div>
-</div>
 
 
 ## Divergence
@@ -145,11 +143,8 @@ $$\begin{aligned}
     }
 \end{aligned}$$
 
-<div class="accordion">
-<input type="checkbox" id="proof-div"/>
-<label for="proof-div">Proof</label>
-<div class="hidden" markdown="1">
-<label for="proof-div">Proof.</label>
+
+{% include proof/start.html id="proof-div" -%}
 As preparation, we rewrite $$\vb{V}$$ as follows
 to introduce the scale factors:
 
@@ -222,8 +217,8 @@ $$\begin{aligned}
 
 After repeating this procedure for the other components of $$\vb{V}$$,
 we get the desired general expression for the divergence.
-</div>
-</div>
+{% include proof/end.html id="proof-div" %}
+
 
 
 ## Laplacian
@@ -246,6 +241,7 @@ $$\begin{aligned}
 \end{aligned}$$
 
 
+
 ## Curl
 
 The curl of a vector $$\vb{V}$$ is as follows
@@ -264,11 +260,8 @@ $$\begin{aligned}
     }
 \end{aligned}$$
 
-<div class="accordion">
-<input type="checkbox" id="proof-curl"/>
-<label for="proof-curl">Proof</label>
-<div class="hidden" markdown="1">
-<label for="proof-curl">Proof.</label>
+
+{% include proof/start.html id="proof-curl" -%}
 The curl is found in a similar way as the divergence.
 We rewrite $$\vb{V}$$ like so:
 
@@ -317,8 +310,8 @@ $$\begin{aligned}
 
 If we go through the same process for the other components of $$\vb{V}$$
 and add up the results, we get the desired expression for the curl.
-</div>
-</div>
+{% include proof/end.html id="proof-curl" %}
+
 
 
 ## Differential elements