http://en.wikipedia.org/wiki/Rosser%27s_trickhttps://en.wikipedia.org/wiki/Rosser%27s_trick
"A technique is a trick that works twice"
Note that Grothendieck never published his proof of the Grothendieck-Riemann-Roch theorem because he felt that the proof depended on an "astuce" (trick) rather than flowing naturally.