<?xml version="1.0" encoding="UTF-8"?>
<math xmlns="http://www.w3.org/1998/Math/MathML">
   <mi> </mi>
   <msub>
      <mfenced close="]" open="[">
         <mi>A</mi>
      </mfenced>
      <mi>t</mi>
   </msub>
   <mo>=</mo>
   <mo>-</mo>
   <mi>k</mi>
   <mi>t</mi>
   <mo>+</mo>
   <msub>
      <mfenced close="]" open="[">
         <mi>A</mi>
      </mfenced>
      <mn>0</mn>
   </msub>
</math>
