I only saw Apostle smile once.
It was Gauss&#x27; birthday, which he always celebrated in April with a cake. It had the Flux Theorem (Divergence to Surface Integral), and I got the &quot;dx&quot; labeled piece.<p>I complained that he had given me the smallest piece, and saw just the hint of a curl to his lips.<p>Hopefully, the &quot;useful theorem&quot;* didn&#x27;t die with him...<p>*Apostle always referred to the useful theorem when proving problems in class... if you could figure it out, you were done.