Hi Haruki,
Thanks for organizing the issue. If the community prefers logback, I will gladly change the dependency and update the PR. However, it has the following issues: 1. The log4j2 vulnerabilities seem mostly fixed, and KIP-653 + KIP-719 are not released yet. So, using log4j2 (whose recent update pace is so high) will not affect the users. 2. To switch to logback, the following features should be reworked: a. Dynamic logger level configuration (core, connect) b. Logging tests (streams) c. Kafka Appender (tools) a and b are the most challenging ones since there is little documentation on how to do this, so it requires analyzing the implementation itself. (what I actually did with log4j2) About c, logback does not provide a Kafka Appender so we have to provide an equivalent. It is why I prefer to use log4j2. How do you think? Thanks, Dongjin On Thu, Dec 23, 2021 at 9:01 AM Haruki Okada <ocadar...@gmail.com> wrote: > Hi, Dongjin, > > Sorry for interrupting the discussion. > And thank you for your hard work about KIP-653, KIP-719. > > I understand that KIP-653 is already accepted so log4j2 is the choice of > the Kafka community though, I'm now feeling that logback is a better choice > here. > > Reasons: > > - even after "log4shell", several vulnerabilities found on log4j2 so new > versions are released and users have to update in high-pace > * actually, a CVE was also reported for logback (CVE-2021-42550) but it > requires edit-permission of the config file for an attacker so it's much > less threatening > - log4j1.x and logback are made by same developer (ceki), so substantially > the successor of log4j1 is logback rather than log4j2 > - in Hadoop project, seems similar suggestion was made from a PMC > * https://issues.apache.org/jira/browse/HADOOP-12956 > > > What do you think about adopting logback instead? > > > Thanks, > > 2021年12月21日(火) 18:02 Dongjin Lee <dong...@apache.org>: > > > Hi Mickael, > > > > > In the meantime, you may want to bump the VOTE thread too. > > > > Sure, I just reset the voting thread with a brief context. > > > > Thanks, > > Dongjin > > > > On Tue, Dec 21, 2021 at 2:13 AM Mickael Maison <mickael.mai...@gmail.com > > > > wrote: > > > > > Thanks Dongjin! > > > > > > I'll take a look soon. > > > In the meantime, you may want to bump the VOTE thread too. > > > > > > Best, > > > Mickael > > > > > > > > > On Sat, Dec 18, 2021 at 10:00 AM Dongjin Lee <dong...@apache.org> > wrote: > > > > > > > > Hi Mickael, > > > > > > > > Finally, I did it! As you can see at the PR > > > > <https://github.com/apache/kafka/pull/10244>, KIP-719 now uses > > log4j2's > > > > Kafka appender, and log4j-appender is not used by the other modules > > > > anymore. You can see how it will work with KIP-653 at this preview > > > > <http://home.apache.org/~dongjin/post/apache-kafka-log4j2-support/>, > > > based > > > > on Apache Kafka 3.0.0. The proposal document > > > > < > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-719%3A+Deprecate+Log4J+Appender > > > > > > > > is also updated accordingly, with its title. > > > > > > > > There is a minor issue on log4j2 > > > > <https://issues.apache.org/jira/browse/LOG4J2-3256>, but it seems > like > > > it > > > > will be resolved soon. > > > > > > > > Best, > > > > Dongjin > > > > > > > > On Wed, Dec 15, 2021 at 9:28 PM Dongjin Lee <dong...@apache.org> > > wrote: > > > > > > > > > Hi Mickael, > > > > > > > > > > > Can we do step 3 without breaking any compatibility? If so then > > that > > > > > sounds like a good idea. > > > > > > > > > > As far as I know, the answer is yes; I am now updating my PR, so I > > will > > > > > notify you as soon as I complete the work. > > > > > > > > > > Best, > > > > > Dongjin > > > > > > > > > > On Wed, Dec 15, 2021 at 2:00 AM Mickael Maison < > > > mickael.mai...@gmail.com> > > > > > wrote: > > > > > > > > > >> Hi Dongjin, > > > > >> > > > > >> Sorry for the late reply. Can we do step 3 without breaking any > > > > >> compatibility? If so then that sounds like a good idea. > > > > >> > > > > >> Thanks, > > > > >> Mickael > > > > >> > > > > >> > > > > >> > > > > >> On Tue, Nov 23, 2021 at 2:08 PM Dongjin Lee <dong...@apache.org> > > > wrote: > > > > >> > > > > > >> > Hi Mickael, > > > > >> > > > > > >> > I also thought over the issue thoroughly and would like to > > propose a > > > > >> minor > > > > >> > change to your proposal: > > > > >> > > > > > >> > 1. Deprecate log4j-appender now > > > > >> > 2. Document how to migrate into logging-log4j2 > > > > >> > 3. (Changed) Replace the log4j-appender (in turn log4j 1.x) > > > > >> dependencies in > > > > >> > tools, trogdor, and shell and upgrade to log4j2 in 3.x, removing > > > log4j > > > > >> 1.x > > > > >> > dependencies. > > > > >> > 4. (Changed) Remove log4j-appender in Kafka 4.0 > > > > >> > > > > > >> > What we need to do for the log4j2 upgrade is just removing the > > log4j > > > > >> > dependencies only, for they can cause a classpath error. And > > > actually, > > > > >> we > > > > >> > can do it without discontinuing publishing the log4j-appender > > > artifact. > > > > >> So, > > > > >> > I suggest separating the upgrade to log4j2 and removing the > > > > >> log4j-appender > > > > >> > module. > > > > >> > > > > > >> > How do you think? If you agree, I will update the KIP and the PR > > > > >> > accordingly ASAP. > > > > >> > > > > > >> > Thanks, > > > > >> > Dongjin > > > > >> > > > > > >> > On Mon, Nov 15, 2021 at 8:06 PM Mickael Maison < > > > > >> mickael.mai...@gmail.com> > > > > >> > wrote: > > > > >> > > > > > >> > > Hi Dongjin, > > > > >> > > > > > > >> > > Thanks for the clarifications. > > > > >> > > > > > > >> > > I wonder if a simpler course of action could be: > > > > >> > > - Deprecate log4j-appender now > > > > >> > > - Document how to use logging-log4j2 > > > > >> > > - Remove log4j-appender and all the log4j dependencies in > Kafka > > > 4.0 > > > > >> > > > > > > >> > > This delays KIP-653 till Kafka 4.0 but (so far) Kafka is not > > > directly > > > > >> > > affected by the log4j CVEs. At least this gives us a clear and > > > simple > > > > >> > > roadmap to follow. > > > > >> > > > > > > >> > > What do you think? > > > > >> > > > > > > >> > > On Tue, Nov 9, 2021 at 12:12 PM Dongjin Lee < > dong...@apache.org > > > > > > > >> wrote: > > > > >> > > > > > > > >> > > > Hi Mickael, > > > > >> > > > > > > > >> > > > I greatly appreciate you for reading the proposal so > > carefully! > > > I > > > > >> wrote > > > > >> > > it > > > > >> > > > quite a while ago and rechecked it today. > > > > >> > > > > > > > >> > > > > Is the KIP proposing to replace the existing log4-appender > > or > > > > >> simply > > > > >> > > add > > > > >> > > > a new one for log4j2? Reading the KIP and with its current > > > title, > > > > >> it's > > > > >> > > not > > > > >> > > > entirely explicit. > > > > >> > > > > > > > >> > > > Oh, After re-reading it, I realized that this is not clear. > > Let > > > me > > > > >> > > clarify; > > > > >> > > > > > > > >> > > > 1. Provide a lo4j2 equivalent of traditional log4j-appender, > > > > >> > > > log4j2-appender. > > > > >> > > > 2. Migrate the modules depending on log4j-appender (i.e., > > tools, > > > > >> trogdor, > > > > >> > > > shell) into log4j2-appender, removing log4j-appender from > > > > >> dependencies. > > > > >> > > > 3. Entirely remove log4j-appender from the project > > dependencies, > > > > >> along > > > > >> > > with > > > > >> > > > log4j. > > > > >> > > > > > > > >> > > > I think log4j-appender may be published for every new > release > > > like > > > > >> > > before, > > > > >> > > > but the committee should make a decision on the policy. > > > > >> > > > > > > > >> > > > > Under Rejected Alternative, the KIP states: "the Kafka > > > appender > > > > >> > > provided > > > > >> > > > by log4j2 community stores log message in the Record key". > > > Looking > > > > >> at the > > > > >> > > > code, it looks like the log message is stored in the Record > > > value: > > > > >> > > > > > > > >> > > > > > > >> > > > > > > https://github.com/apache/logging-log4j2/blob/master/log4j-kafka/src/main/java/org/apache/logging/log4j/kafka/appender/KafkaManager.java#L135 > > > > >> > > > Am I missing something? > > > > >> > > > > > > > >> > > > It's totally my fault; I confused it with another appender. > > The > > > > >> > > > compatibility problem in the logging-log4j2 Kafka appender > is > > > not > > > > >> the > > > > >> > > > format but the configuration. logging-log4j2 Kafka appender > > > supports > > > > >> > > > `properties` configuration, which will be directly used to > > > > >> instantiate a > > > > >> > > > Kafka producer. However, log4j-appender has been using > > > non-producer > > > > >> > > config > > > > >> > > > names like brokerList (=bootstrap.servers), requiredNumAcks > > > (=acks). > > > > >> > > > Instead, logging-log4j2 Kafka appender supports retryCount, > > > > >> > > > sendEventTimestamp. > > > > >> > > > > > > > >> > > > On second thought, using logging-log4j2 Kafka appender > > > internally > > > > >> and > > > > >> > > > making log4j2-appender to focus on compatibility facade only > > > would > > > > >> be a > > > > >> > > > better approach; As I described above, the goal of this > module > > > is > > > > >> just > > > > >> > > > keeping the backward-compatibility, and (as you pointed out) > > the > > > > >> current > > > > >> > > > implementation has little value. Since > > > > >> > > org.apache.logging.log4j:log4j-core > > > > >> > > > already includes Kafka appender, we can make use of the > > 'proven > > > > >> wheel' > > > > >> > > > without adding more dependencies. I have not tried it yet, > > but I > > > > >> think it > > > > >> > > > is well worth it. (One additional advantage of this approach > > is > > > > >> > > providing a > > > > >> > > > bridge to the users who hope to move from/into > logging-log4j2 > > > Kafka > > > > >> > > > appender.) > > > > >> > > > > > > > >> > > > > As the current log4j-appender is not even deprecated yet, > in > > > > >> theory we > > > > >> > > > can't remove it till Kafka 4. If we want to speed up the > > > process, I > > > > >> > > wonder > > > > >> > > > if the lack of documentation and a migration guide could > help > > > us. > > > > >> What do > > > > >> > > > you think? > > > > >> > > > > > > > >> > > > In fact, this is what I am doing nowadays. While working > with > > > > >> > > > log4j-appender, I found that despite a lack of > documentation, > > > > >> > > considerable > > > > >> > > > users are already using it[^1][^2][^3][^4][^5]. So, I think > > > > >> providing a > > > > >> > > > documentation to those who are already using log4j-appender > is > > > > >> > > > indispensable. It should include: > > > > >> > > > > > > > >> > > > - What is the difference between log4j-appender vs. > > > log4j2-appender. > > > > >> > > > - Which options are supported and deprecated. > > > > >> > > > - Exemplar configurations that show how to migrate. > > > > >> > > > > > > > >> > > > Here is the summary: > > > > >> > > > > > > > >> > > > 1. The goal of this proposal is to replace the traditional > > > > >> log4j-appender > > > > >> > > > for compatibility concerns. But log4j-appender may be > > published > > > > >> after the > > > > >> > > > deprecation. > > > > >> > > > 2. As of present, the description about logging-log4j2 Kafka > > > > >> appender is > > > > >> > > > entirely wrong. The problem is interface compatibility, not > > > record > > > > >> > > format. > > > > >> > > > Focusing on the compatibility facade is a good approach. > > > > >> > > > 3. A documentation focus on migration should be provided. > > > > >> > > > > > > > >> > > > If you have any questions or suggestions, don't hesitate to > > > tell me. > > > > >> > > Thanks > > > > >> > > > again for your comments! > > > > >> > > > > > > > >> > > > Best, > > > > >> > > > Dongjin > > > > >> > > > > > > > >> > > > [^1]: > > > > >> > > > > > > > >> > > > > > > >> > > > > > > https://docs.cloudera.com/csa/1.2.0/monitoring/topics/csa-kafka-logging.html > > > > >> > > > [^2]: > > > > >> > > > > > > > >> > > > > > > >> > > > > > > https://stackoverflow.com/questions/22034895/how-to-use-kafka-0-8-log4j-appender > > > > >> > > > [^3]: > > > > >> > > > > > > > >> > > > > > > >> > > > > > > https://stackoverflow.com/questions/32402405/delay-in-kafka-log4j-appender > > > > >> > > > [^4]: > > > > >> > > > > > > > >> > > > > > > >> > > > > > > https://stackoverflow.com/questions/32301129/kafka-log4j-appender-not-sending-messages > > > > >> > > > [^5]: > > > > >> > > > > > > > >> > > > > > > >> > > > > > > https://stackoverflow.com/questions/35628706/kafka-log4j-appender-0-9-does-not-work > > > > >> > > > > > > > >> > > > On Mon, Nov 8, 2021 at 9:04 PM Mickael Maison < > > > > >> mickael.mai...@gmail.com> > > > > >> > > > wrote: > > > > >> > > > > > > > >> > > > > Hi Dongjin, > > > > >> > > > > > > > > >> > > > > Thanks for working on the update to log4j2, it's > > definitively > > > > >> > > > > something we should complete. > > > > >> > > > > I have a couple of comments: > > > > >> > > > > > > > > >> > > > > 1) Is the KIP proposing to replace the existing > > log4-appender > > > or > > > > >> > > > > simply add a new one for log4j2? Reading the KIP and with > > its > > > > >> current > > > > >> > > > > title, it's not entirely explicit. For example I don't > see a > > > > >> statement > > > > >> > > > > under the proposed changes section. The PR seems to only > add > > > a new > > > > >> > > > > appender but the KIP mentions we want to fully remove > > > > >> dependencies to > > > > >> > > > > log4j. > > > > >> > > > > > > > > >> > > > > 2) Under Rejected Alternative, the KIP states: "the Kafka > > > appender > > > > >> > > > > provided by log4j2 community stores log message in the > > Record > > > > >> key". > > > > >> > > > > Looking at the code, it looks like the log message is > stored > > > in > > > > >> the > > > > >> > > > > Record value: > > > > >> > > > > > > > > >> > > > > > > >> > > > > > > https://github.com/apache/logging-log4j2/blob/master/log4j-kafka/src/main/java/org/apache/logging/log4j/kafka/appender/KafkaManager.java#L135 > > > > >> > > > > Am I missing something? > > > > >> > > > > Comparing it with the proposed new appender, apart from > > their > > > > >> > > > > configuration format (hence the backwards compatibility > > > issues), > > > > >> they > > > > >> > > > > both work pretty much the same way, so it's not clear it > > would > > > > >> add a > > > > >> > > > > ton a value. > > > > >> > > > > > > > > >> > > > > At a glance, _I've not extensively looked at it_, it does > > not > > > look > > > > >> > > > > very hard to migrate to the appender from the logging > team. > > I > > > was > > > > >> > > > > wondering if we should mention it in our documentation > but I > > > was > > > > >> not > > > > >> > > > > able to find any references to the log4j-appender in the > > Kafka > > > > >> docs: > > > > >> > > > > > > > https://github.com/apache/kafka-site/search?q=KafkaLog4jAppender > > > > >> > > > > > > > > >> > > > > As the current log4j-appender is not even deprecated yet, > in > > > > >> theory we > > > > >> > > > > can't remove it till Kafka 4. If we want to speed up the > > > process, > > > > >> I > > > > >> > > > > wonder if the lack of documentation and a migration guide > > > could > > > > >> help > > > > >> > > > > us. What do you think? > > > > >> > > > > > > > > >> > > > > Thanks, > > > > >> > > > > Mickael > > > > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > > On Fri, Jun 11, 2021 at 4:57 PM Boojapho O < > > > booja...@gmail.com> > > > > >> wrote: > > > > >> > > > > > > > > > >> > > > > > Continuing to use log4j would leave several known > security > > > > >> > > > > vulnerabilities in Apache Kafka, including > > > > >> > > > > https://nvd.nist.gov/vuln/detail/CVE-2019-17571. The > > Apache > > > > >> log4j > > > > >> > > team > > > > >> > > > > will not fix this vulnerability and is urging an upgrade > to > > > > >> log4j2. > > > > >> > > See > > > > >> > > > > https://logging.apache.org/log4j/1.2/ for further > > > information. > > > > >> > > > > > > > > > >> > > > > > This is desperately needed in Apache 3.0 to keep the > > > software > > > > >> secure. > > > > >> > > > > > > > > > >> > > > > > On 2021/05/26 12:31:20, Dongjin Lee <dong...@apache.org > > > > > wrote: > > > > >> > > > > > > CC'd the +1ers of KIP-653 with detailed context: > > > > >> > > > > > > > > > > >> > > > > > > When I submitted and got the approval of KIP-653: > > Upgrade > > > > >> log4j to > > > > >> > > > > log4j2 > > > > >> > > > > > > < > > > > >> > > > > > > > > >> > > > > > > >> > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-653%3A+Upgrade+log4j+to+log4j2 > > > > >> > > > > >, > > > > >> > > > > > > I thought the log4j2-appender should not be the scope > of > > > the > > > > >> work. > > > > >> > > But > > > > >> > > > > it > > > > >> > > > > > > was wrong. > > > > >> > > > > > > > > > > >> > > > > > > Since the VerifiableLog4jAppender tool is built upon > > > > >> > > log4j-appender, > > > > >> > > > > log4j > > > > >> > > > > > > 1.x artifact will co-exist with log4j2 artifact in the > > > > >> classpath > > > > >> > > within > > > > >> > > > > > > this scheme. Since the log4j 1.x code is not called > > > anymore, I > > > > >> > > thought > > > > >> > > > > it > > > > >> > > > > > > is not problematic but actually, it was not - when I > > > started > > > > >> to > > > > >> > > > > provide a > > > > >> > > > > > > preview of KIP-653 > > > > >> > > > > > > < > > > > >> http://home.apache.org/~dongjin/post/apache-kafka-log4j2-support/ > > > > >> > > >, > > > > >> > > > > some > > > > >> > > > > > > users reported that sometimes slf4j fails to find the > > > > >> appropriate > > > > >> > > > > binding > > > > >> > > > > > > within the classpath, resulting fail to append the log > > > > >> message. > > > > >> > > > > > > > > > > >> > > > > > > To resolve this problem, I subtly adjusted the scope > of > > > the > > > > >> work; I > > > > >> > > > > > > excluded Tools and Trogdor from KIP-653 and extended > > > KIP-719 > > > > >> to > > > > >> > > take > > > > >> > > > > care > > > > >> > > > > > > of them instead, along with providing log4j2-appender. > > It > > > is > > > > >> why > > > > >> > > the > > > > >> > > > > > > current WIP implementations include some classpath > logic > > > in > > > > >> the > > > > >> > > shell > > > > >> > > > > > > script and *why KIP-653 only can't complete the log4j2 > > > > >> migration*. > > > > >> > > > > > > > > > > >> > > > > > > I hope you will check this proposal out. > > > > >> > > > > > > > > > > >> > > > > > > Best, > > > > >> > > > > > > Dongjin > > > > >> > > > > > > > > > > >> > > > > > > On Tue, May 25, 2021 at 10:43 PM Dongjin Lee < > > > > >> dong...@apache.org> > > > > >> > > > > wrote: > > > > >> > > > > > > > > > > >> > > > > > > > Bumping up the discussion thread. > > > > >> > > > > > > > > > > > >> > > > > > > > Recently, I updated the document of KIP-653: Upgrade > > > log4j > > > > >> to > > > > >> > > log4j2 > > > > >> > > > > > > > < > > > > >> > > > > > > > > >> > > > > > > >> > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-653%3A+Upgrade+log4j+to+log4j2 > > > > >> > > > > > > > >> > > > > (accepted) > > > > >> > > > > > > > and KIP-719: Add Log4J2 Appender > > > > >> > > > > > > > < > > > > >> > > > > > > > > >> > > > > > > >> > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-719%3A+Add+Log4J2+Appender > > > > >> > > > > > > > >> > > > > (under > > > > >> > > > > > > > discussion) reflecting the recent changes to our > > > codebase. > > > > >> > > > > Especially: > > > > >> > > > > > > > > > > > >> > > > > > > > 1. KIP-653 document > > > > >> > > > > > > > < > > > > >> > > > > > > > > >> > > > > > > >> > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-653%3A+Upgrade+log4j+to+log4j2 > > > > >> > > > > > > > >> > > > > now > > > > >> > > > > > > > explains which modules will be migrated and why. > > > > >> > > > > > > > 2. KIP-719 document > > > > >> > > > > > > > < > > > > >> > > > > > > > > >> > > > > > > >> > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-719%3A+Add+Log4J2+Appender > > > > >> > > > > > > > >> > > > > now > > > > >> > > > > > > > explains not only the log4j2-appender plan but also > > > > >> upgrading the > > > > >> > > > > omitted > > > > >> > > > > > > > modules in KIP-653 into log4j2. > > > > >> > > > > > > > > > > > >> > > > > > > > As you can see here, those two KIPs are the > different > > > parts > > > > >> of > > > > >> > > the > > > > >> > > > > same > > > > >> > > > > > > > problem. I believe the community will have a good > > grasp > > > on > > > > >> why > > > > >> > > both > > > > >> > > > > KIPs > > > > >> > > > > > > > are best if released altogether. > > > > >> > > > > > > > > > > > >> > > > > > > > I will open the voting thread now, and please leave > a > > > vote > > > > >> if > > > > >> > > you are > > > > >> > > > > > > > interested in this issue. > > > > >> > > > > > > > > > > > >> > > > > > > > Best, > > > > >> > > > > > > > Dongjin > > > > >> > > > > > > > > > > > >> > > > > > > > On Tue, Mar 2, 2021 at 5:00 PM Dongjin Lee < > > > > >> dong...@apache.org> > > > > >> > > > > wrote: > > > > >> > > > > > > > > > > > >> > > > > > > >> Hi Kafka dev, > > > > >> > > > > > > >> > > > > >> > > > > > > >> I would like to start the discussion of KIP-719: > Add > > > Log4J2 > > > > >> > > > > Appender. > > > > >> > > > > > > >> > > > > >> > > > > > > >> > > > > >> > > > > > > >> > > > > >> > > > > > > > > >> > > > > > > >> > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-719%3A+Add+Log4J2+Appender > > > > >> > > > > > > >> > > > > >> > > > > > > >> All kinds of feedbacks are greatly appreciated! > > > > >> > > > > > > >> > > > > >> > > > > > > >> Best, > > > > >> > > > > > > >> Dongjin > > > > >> > > > > > > >> > > > > >> > > > > > > >> -- > > > > >> > > > > > > >> *Dongjin Lee* > > > > >> > > > > > > >> > > > > >> > > > > > > >> *A hitchhiker in the mathematical world.* > > > > >> > > > > > > >> > > > > >> > > > > > > >> > > > > >> > > > > > > >> > > > > >> > > > > > > >> *github: <http://goog_969573159/> > > > github.com/dongjinleekr > > > > >> > > > > > > >> <https://github.com/dongjinleekr>keybase: > > > > >> > > > > https://keybase.io/dongjinleekr > > > > >> > > > > > > >> <https://keybase.io/dongjinleekr>linkedin: > > > > >> > > > > kr.linkedin.com/in/dongjinleekr > > > > >> > > > > > > >> <https://kr.linkedin.com/in/dongjinleekr > > >speakerdeck: > > > > >> > > > > speakerdeck.com/dongjin > > > > >> > > > > > > >> <https://speakerdeck.com/dongjin>* > > > > >> > > > > > > >> > > > > >> > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > -- > > > > >> > > > > > > > *Dongjin Lee* > > > > >> > > > > > > > > > > > >> > > > > > > > *A hitchhiker in the mathematical world.* > > > > >> > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > *github: <http://goog_969573159/> > > > github.com/dongjinleekr > > > > >> > > > > > > > <https://github.com/dongjinleekr>keybase: > > > > >> > > > > https://keybase.io/dongjinleekr > > > > >> > > > > > > > <https://keybase.io/dongjinleekr>linkedin: > > > > >> > > > > kr.linkedin.com/in/dongjinleekr > > > > >> > > > > > > > <https://kr.linkedin.com/in/dongjinleekr > >speakerdeck: > > > > >> > > > > speakerdeck.com/dongjin > > > > >> > > > > > > > <https://speakerdeck.com/dongjin>* > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > -- > > > > >> > > > > > > *Dongjin Lee* > > > > >> > > > > > > > > > > >> > > > > > > *A hitchhiker in the mathematical world.* > > > > >> > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > *github: <http://goog_969573159/> > > github.com/dongjinleekr > > > > >> > > > > > > <https://github.com/dongjinleekr>keybase: > > > > >> > > > > https://keybase.io/dongjinleekr > > > > >> > > > > > > <https://keybase.io/dongjinleekr>linkedin: > > > > >> > > > > kr.linkedin.com/in/dongjinleekr > > > > >> > > > > > > <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: > > > > >> > > > > speakerdeck.com/dongjin > > > > >> > > > > > > <https://speakerdeck.com/dongjin>* > > > > >> > > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > > >> > > > -- > > > > >> > > > *Dongjin Lee* > > > > >> > > > > > > > >> > > > *A hitchhiker in the mathematical world.* > > > > >> > > > > > > > >> > > > > > > > >> > > > > > > > >> > > > *github: <http://goog_969573159/>github.com/dongjinleekr > > > > >> > > > <https://github.com/dongjinleekr>keybase: > > > > >> > > https://keybase.io/dongjinleekr > > > > >> > > > <https://keybase.io/dongjinleekr>linkedin: > > > > >> > > kr.linkedin.com/in/dongjinleekr > > > > >> > > > <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: > > > > >> > > speakerdeck.com/dongjin > > > > >> > > > <https://speakerdeck.com/dongjin>* > > > > >> > > > > > > >> > > > > > >> > > > > > >> > -- > > > > >> > *Dongjin Lee* > > > > >> > > > > > >> > *A hitchhiker in the mathematical world.* > > > > >> > > > > > >> > > > > > >> > > > > > >> > *github: <http://goog_969573159/>github.com/dongjinleekr > > > > >> > <https://github.com/dongjinleekr>keybase: > > > > >> https://keybase.io/dongjinleekr > > > > >> > <https://keybase.io/dongjinleekr>linkedin: > > > > >> kr.linkedin.com/in/dongjinleekr > > > > >> > <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: > > > > >> speakerdeck.com/dongjin > > > > >> > <https://speakerdeck.com/dongjin>* > > > > >> > > > > > > > > > > > > > > > -- > > > > > *Dongjin Lee* > > > > > > > > > > *A hitchhiker in the mathematical world.* > > > > > > > > > > > > > > > > > > > > *github: <http://goog_969573159/>github.com/dongjinleekr > > > > > <https://github.com/dongjinleekr>keybase: > > > https://keybase.io/dongjinleekr > > > > > <https://keybase.io/dongjinleekr>linkedin: > > > kr.linkedin.com/in/dongjinleekr > > > > > <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: > > > speakerdeck.com/dongjin > > > > > <https://speakerdeck.com/dongjin>* > > > > > > > > > > > > > > > > > -- > > > > *Dongjin Lee* > > > > > > > > *A hitchhiker in the mathematical world.* > > > > > > > > > > > > > > > > *github: <http://goog_969573159/>github.com/dongjinleekr > > > > <https://github.com/dongjinleekr>keybase: > > > https://keybase.io/dongjinleekr > > > > <https://keybase.io/dongjinleekr>linkedin: > > > kr.linkedin.com/in/dongjinleekr > > > > <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: > > > speakerdeck.com/dongjin > > > > <https://speakerdeck.com/dongjin>* > > > > > > > > > -- > > *Dongjin Lee* > > > > *A hitchhiker in the mathematical world.* > > > > > > > > *github: <http://goog_969573159/>github.com/dongjinleekr > > <https://github.com/dongjinleekr>keybase: > https://keybase.io/dongjinleekr > > <https://keybase.io/dongjinleekr>linkedin: > kr.linkedin.com/in/dongjinleekr > > <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: > > speakerdeck.com/dongjin > > <https://speakerdeck.com/dongjin>* > > > > > -- > ======================== > Okada Haruki > ocadar...@gmail.com > ======================== > -- *Dongjin Lee* *A hitchhiker in the mathematical world.* *github: <http://goog_969573159/>github.com/dongjinleekr <https://github.com/dongjinleekr>keybase: https://keybase.io/dongjinleekr <https://keybase.io/dongjinleekr>linkedin: kr.linkedin.com/in/dongjinleekr <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: speakerdeck.com/dongjin <https://speakerdeck.com/dongjin>*
