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I'm confused by the following trivial code:

{Range[0, 1, .1][[8]]} === {.7}

gives True

MemberQ[{.7}, .7]

gives True, but

MemberQ[{Range[0, 1, .1][[8]]}, .7]

gives False. Huh? What am I missing?

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    $\begingroup$ {Range[0, 1, .1][[8]], .7} // InputForm ought to be enlightening. Moral lesson is that you don't do such pattern matches on inexact numbers. $\endgroup$ – J. M.'s ennui♦ Aug 6 '17 at 12:53
  • $\begingroup$ @J.M. thanks, I thought it might be a floating point thing, but then I was surprised by the first equality, which I still don't understand $\endgroup$ – bjorne Aug 6 '17 at 12:55
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    $\begingroup$ That would be due to Internal`$SameQTolerance (or Internal`$EqualTolerance if you had used ==). See e.g. this. $\endgroup$ – J. M.'s ennui♦ Aug 6 '17 at 12:59
  • $\begingroup$ @J.M. Great, thanks! $\endgroup$ – bjorne Aug 6 '17 at 13:00
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    $\begingroup$ Recommended reading: (5149), (5580), (21711), (66386), (86815). Please take a look at these and tell me if you feel that your question is adequately addressed in these. If so we can mark it as such. $\endgroup$ – Mr.Wizard Aug 6 '17 at 17:07