I was once salvaging old mesquite fence posts for firewood, and the mesquite would dull our chain saw to the point where a resharpened chain was needed about every third log.  I figured I was going to have a tough job cutting the logs to fireplace length with my swede saw...
No problem.  The saw went through the mesquite like a hot knife through butter.  I do keep a small one in my vehicle all the time.
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Geezer in Chief