Context-Free Languages in 3.5 Hours (CFG, PDA, Conversions, Closure, Pumping Lemma)
ฝัง
- เผยแพร่เมื่อ 4 ก.ค. 2024
- Here we do a livestream covering everything to do with context-free languages. We cover context-free grammars (CFGs and two examples), pushdown automata (PDAs), the conversion from a CFG to a PDA, the conversion from a PDA to a CFG, the pumping lemma for context-free languages, and closure properties (as well as operations CFLs are not closed under).
Timestamps:
0:00 - Start of livestream
21:19 - Start of topics
24:10 - Definition of CFG
31:20 - Example 1 of CFG (with definitions)
41:30 - Example 2 of CFG (balanced parentheses)
47:30 - CFLs closed under union, concat, star
59:40 - Chomsky Normal Form definition
1:09:11 - CFG to CNF start
1:13:38 - Step 1 of CNF conversion
1:15:22 - Step 2 of CNF conversion
1:20:05 - Step 3 of CNF conversion
1:23:53 - Step 4 of CNF conversion
1:28:12 - Step 5 of CNF conversion
1:39:50 - PDA definition
1:45:00 - PDA example
1:49:50 - CFG to PDA
2:01:10 - PDA to CFG
2:36:30 - Proof of Pumping Lemma for CFLs
2:55:40 - Pumping Lemma for CFLs statement
2:58:50 - Proving {0^n 1^n 2^n} is not a CFL
3:07:40 - CFLs not closed under complement or intersection
3:23:10 - Wrapup
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Timestamps:
0:00 - Start of livestream
21:19 - Start of topics
24:10 - Definition of CFG
31:20 - Example 1 of CFG (with definitions)
41:30 - Example 2 of CFG (balanced parentheses)
47:30 - CFLs closed under union, concat, star
59:40 - Chomsky Normal Form definition
1:09:11 - CFG to CNF start
1:13:38 - Step 1 of CNF conversion
1:15:22 - Step 2 of CNF conversion
1:20:05 - Step 3 of CNF conversion
1:23:53 - Step 4 of CNF conversion
1:28:12 - Step 5 of CNF conversion
1:39:50 - PDA definition
1:45:00 - PDA example
1:49:50 - CFG to PDA
2:01:10 - PDA to CFG
2:36:30 - Proof of Pumping Lemma for CFLs
2:55:40 - Pumping Lemma for CFLs statement
2:58:50 - Proving {0^n 1^n 2^n} is not a CFL
3:07:40 - CFLs not closed under complement or intersection
3:23:10 - Wrapup
Thanks sir for these great lectures
You saved my life, thank you sir!
This was incredibly helpful, you explained everything so well. Thank you so much.
This pumping lemma explanation is the first time it made any sense to me after taking my school's intro to theory course this whole semester. Thank you for making these videos
YOU'RE GOATED
3 hrs until my exam. I am not sleeping today. Video is looking great till now . Before seeing your video i was praying for getting passed,and 1 hr into your video i am thinking may be i can get 90 percent ;)
I usually have adblock on, but I turned it off completely for your channel, maybe you can tell other people to consider doing the same to contribute a bit more for free! I hope you grow bigger and help many more future computer scientists!!
Thanks very much! You don't have to turn off adblock though as one viewer's doing that only yields a tiny amount of money lol. Might as well have an ad-free experience if you already have it on.
I do hope the channel grows much more substantially this year. Thanks very much for your support though!
@@EasyTheory yeah I'll probably just turn it back on as I'm getting far more ads than expected and might just donate something later, which is more direct. Also, I love when you discover the example at 2:10:50 as you actually look excited to be able to use it with your students, it really shows your commitment as a teacher :)
@@pere_gin totes understand (and I do the same lol). I put the ad breaks in there, but sometimes they skip if you've seen a "lot" of them I think.
I really like that example, because I've always thought it was just a "pull out of thin air" proof, but if you really think about it it's a lot simpler than at first glance.
I have 1 hour 21 minutes until the exam, 2x speed for the win
Good luck!
@@EasyTheory Thank you!
@@EasyTheory BTW. The exam went great, your vids totally saved me
hope it was good
Does it not matter if you switch the order of step 4 and step 5 of the CNF conversion?
2:00:20 How can you pop something "epsilon, 1 or 0" when they are not in the stack. Or am I wrong and every time what something is read it is popped ?
1:49:50