Youtor
13 Disequality
YOUR LINK HERE:
http://youtube.com/watch?v=5tA7ejHcfNM
In this video we see, for the first time, how to apply a pre-existing lemma. • The example is simple, to show that n does not equal 5, if n is known to be less than 5. We make use of a lemma ne_of_lt, which allow us to prove a less than goal instead of the not equal goal. • We also explain why `exact` might be better than `apply` in some scenarios. • We also have a first taste of finding lemmas, in this case for the exercise at the end. • Blog: https://leanfirststeps.blogspot.com/2... • GitHub: https://github.com/rzeta0/Lean-First-... • 00:00 - Lemmas • 02:18 - Task • 07:33 - Maths Proof • 09:30 - Lean Proof (Live Coding) • 14:50 - exact vs apply • 16:48 - Review • 24:12 - Easy Exercise (incl Loogle)
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