diff --git a/docs/index.html b/docs/index.html
index b750205..7e19235 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -31,7 +31,7 @@ <h1>Mathup</h1>
       <div class="input">
         <p><label for="try-input">You write…</label></p>
 
-        <textarea id="try-input">bb E[X] = int_(-oo)^oo x f(x)  dx</textarea>
+        <textarea id="try-input">E[X] = int_(-oo)^oo x f(x)  dx</textarea>
 
         <div class="options">
           <label for="try-decimalmark">Decimal mark</label>
@@ -1001,7 +1001,7 @@ <h3>Operators</h3>
               <li>
                 <!-- prettier-ignore -->
                 <use-example>
-                  sum_(n=0)^k a_n = a_0 + a_i + cdots + a_k
+                  sum_(n=0)^k a_n = a_0 + a_1 + cdots + a_k
                 </use-example>
               </li>
               <li>
@@ -1787,6 +1787,10 @@ <h3>Fenced Groups</h3>
                 </use-example>
               </li>
 
+              <li>
+                <use-example> |(Psi(t):) = int Psi(x, t) |(x:) dx </use-example>
+              </li>
+
               <li>
                 <!-- prettier-ignore -->
                 <use-example>
diff --git a/docs/main.js b/docs/main.js
index 9de5e9c..341511b 100644
--- a/docs/main.js
+++ b/docs/main.js
@@ -89,6 +89,31 @@ function removePolyfill(outputEl, mathupEl) {
   }
 }
 
+const DEMO_EQUATIONS = [
+  "E[X] = int_(-oo)^oo x f(x)  dx",
+  "sum_(n=0)^k a_n = a_0 + a_1 + cdots + a_k",
+  "e = sum_(n=0)^oo 1 / n!",
+  "vec x = a hat i + b hat j + c hat k",
+  "grad f(x,y) = ((del f)/(del x) (x, y), (del f)/(del y)(x,y))",
+  "oint_(del S) bf F * d bf s = dint_S grad xx bf F * d bf s",
+  "cc N(x | μ, σ^2) = 1 / (σ sqrt(2π)) e^(-1/2 (x-μ / σ)^2)",
+  "`Gamma`(theta | alpha, beta) = beta^alpha / Gamma(alpha) theta^(alpha - 1) e^(-beta theta)",
+  "P(A | B) = P(B | A)P(A) / P(B)",
+  String.raw`phi =.^\def a/b = a+b / a`,
+  "binom(n, k) = n! / k!(n-k)!",
+  "|(Psi(t):) = int Psi(x, t) |(x:)  dx",
+  "<<V(t)^2>> = lim_(T->oo) 1/T int_(-T/2)^(T/2) V(t)^2  dt",
+  `[λ_0, λ_1, ...;] [p_(0 0), p_(0 1), ...
+                  p_(1 0), p_(1 1), ...
+                  vdots,   vdots,   ddots]`,
+  "||(bf x)||^2 = [x_1 ; x_2 ; x_3]*[x_1 ; x_2 ; x_3]",
+  `n! = { 1,       if n=0 or n=1
+       n(n-1)!, if n > 1`,
+  "x = -b+-sqrt(b^2 - 4ac) / 2a",
+  "ln x = int_1^x 1/t  dt",
+  "bf F @ bf G:  U sube RR^3 -> RR^2",
+];
+
 /**
  * @returns {void}
  */
@@ -138,6 +163,9 @@ function setupPlayground() {
     return;
   }
 
+  tryInput.value =
+    DEMO_EQUATIONS[Math.floor(Math.random() * DEMO_EQUATIONS.length)];
+
   const tryMathUp = /** @type {MathUpElement} */ (
     tryOutput.querySelector("math-up")
   );