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+#+COLUMNS: %40ITEM %10BEAMER_env(Env) %9BEAMER_envargs(Env Args) %10BEAMER_act(Act) %4BEAMER_col(Col) %10BEAMER_extra(Extra) %8BEAMER_opt(Opt)
+#+INCLUDE: "prelude.org" :minlevel 1
+
+* VCS history
+  :PROPERTIES:
+  :CUSTOM_ID: main
+  :END:
+** Evolution of software development
+  :PROPERTIES:
+  :CUSTOM_ID: timeline
+  :END:
+*** Version control system (VCS)
+    - records changes made to a (set of) /source code file/ (s)
+    - allows to operate on versions: diff/merge/fork/recover etc.
+    - *essential* tool for software development
+ #+BEAMER: \pause
+*** Three decades of evolution
+#+LATEX: \centering
+#+LATEX:  \includegraphics[width=.8\linewidth]{VCS_history_timeline.png}
+
+** In a picture \hfill (from https://github.com/progit/progit2)
+  :PROPERTIES:
+  :CUSTOM_ID: vcs-explained
+  :END:
+       #+BEGIN_EXPORT latex
+        \centering\forcebeamerstart
+        \only<1>{\colorbox{white}{\includegraphics[width=\extblockscale{.5\linewidth}]{localvcs}}\mbox{}\\[2em]
+        \texttt{co -r1.2 file.c}
+        }
+        \only<2>{\colorbox{white}{\includegraphics[width=\extblockscale{.5\linewidth}]{centralisedvcs}}\mbox{}\\[2em]
+        \texttt{cvs co -r Rel-1A ProgABC}
+        }
+        \only<3>{\colorbox{white}{\includegraphics[width=\extblockscale{.5\linewidth}]{distvcs}}\mbox{}\\[2em]
+        \texttt{git checkout df3b1b08f756569eff0919e37d8af1f403515b31}
+        }
+        \forcebeamerend
+        #+END_EXPORT
+** Foundations of modern DVCS
+  :PROPERTIES:
+  :CUSTOM_ID: dvcs-to-merkle
+  :END:
+**** Requirements for the D in DVCS
+     - *intrinsic* unique identifiers... \hfill (here: /cryptographic signature/, aka "hash")
+     - ... that work for *tree structures* (software directories)
+     #+BEAMER: \pause
+     # R. C. Merkle, A digital signature based on a conventional encryption
+     # function, Crypto '87
+**** Merkle tree to the rescue (R. C. Merkle, Crypto 1979)       :B_picblock:
+     :PROPERTIES:
+     :BEAMER_opt: pic=merkle, leftpic=true, width=.7\linewidth
+     :BEAMER_env: picblock
+     :BEAMER_act:
+     :END:
+     Combination of
+      - tree
+      - hash function
+** A massive adoption
+  :PROPERTIES:
+  :CUSTOM_ID: adoption
+  :END:
+***  Stack Overflow \hfill \href{https://insights.stackoverflow.com/survey/2018}{[Survey 2018]}
+    :PROPERTIES:
+    :BEAMER_col: 0.47
+    :BEAMER_env: block
+    :END:
+   #+latex: \centering
+   #+ATTR_LATEX: :width \extblockscale{1.4\linewidth}
+   file:stackoverflow-survey-VCS.png
+
+   #+BEAMER: \pause
+*** In numbers
+    :PROPERTIES:
+    :BEAMER_col: 0.45
+    :BEAMER_env: block
+    :END:
+    GitHub \hfill  \href{https://octoverse.github.com/2017/}{[Octoverse 2017]} \href{https://github.blog/2018-11-08-100m-repos/}{[Blog 2018]}
+    - *100.000.000+* repositories
+    - *40.000.000+* developers worldwide
+
+   Bitbucket  \hfill  \href{https://bitbucket.org/blog/celebrating-10-million-bitbucket-cloud-registered-users}{[Blog 2019]}
+    - *28.000.000+* repositories
+    - *10.000.000+* developers worldwide
+
+    GitLab \hfill \href{https://about.gitlab.com/blog/2019/06/06/1-mil-merge-requests/}{[Blog 2019]}
+    - *1.000.000* MRs March 19'
+ #+BEAMER: \pause
+
+*** 
+    \hfill Let's use it!
+