diff --git a/talks-public/2017-10-26-force11/2017-10-26-force11.org b/talks-public/2017-10-26-force11/2017-10-26-force11.org
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--- a/talks-public/2017-10-26-force11/2017-10-26-force11.org
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@@ -1,120 +1,123 @@
 #+COLUMNS: %40ITEM %10BEAMER_env(Env) %9BEAMER_envargs(Env Args) %10BEAMER_act(Act) %4BEAMER_col(Col) %10BEAMER_extra(Extra) %8BEAMER_opt(Opt)
 #+TITLE: Identifying 4 billion source code files
 #+SUBTITLE: Intrinsic identifiers, the Software Heritage experience
 # does not allow short title, so we override it for beamer as follows :
 #+BEAMER_HEADER: \author[Stefano Zacchiroli]{Stefano Zacchiroli}
 #+AUTHOR: Stefano Zacchiroli (Software Heritage, Inria)
 #+DATE: October 26, 2017
 #+EMAIL: zack@upsilon.cc
 
 #
 # Prelude contains all the information needed to export the main beamer latex source
 #
 
 #+INCLUDE: "../../common/modules/prelude.org" :minlevel 1
 #+INCLUDE: "../../common/modules/169.org"
 #+BEAMER_HEADER: \institute[Software Heritage]{University Paris Diderot \& Inria\\\href{mailto:zack@upsilon.cc}{\tt zack@upsilon.cc}}
 
 * Software Heritage
   #+INCLUDE: "../../common/modules/swh-overview-sourcecode.org::#mission" :minlevel 2
 ** Our principles
 #+latex: \begin{center}
 #+ATTR_LATEX: :width .7\linewidth
 file:SWH-as-foundation-slim.png
 #+latex: \end{center}
 #+BEAMER: \pause
 *** Open approach                                             :B_block:BMCOL:
     :PROPERTIES:
     :BEAMER_col: 0.3
     :BEAMER_env: block
     :END:
     open source, transparency
 *** Unix philosophy                         :B_block:BMCOL:noexport:noexport:
     :PROPERTIES:
     :BEAMER_opt:
     :BEAMER_env: block
     :BEAMER_col: 0.3
     :END:
     - do /one/ thing
     - do it /well/
 *** In for the long haul                                      :B_block:BMCOL:
     :PROPERTIES:
     :BEAMER_col: 0.3
     :BEAMER_env: block
     :END:
     non profit, replication
  #+INCLUDE: "../../common/modules/status-extended.org::#archive" :minlevel 2
 * The quest for a PID
 ** Our challenge in the PID arena
 *** Long term
     Identifiers must be there for the long term
 *** No middle man
     Identifiers must be meaningful even if resolvers go away
 *** Integrity, not just naming
     Identifier must ensure that the retrieved object is the intended one
 *** Uniqueness by design
     only one name for each object, each object has only one name
 ** Exploring the PID landscape
 *** A lot of options out there...
     URL, URI, PURL, URN, ARK, DOI, ...
 *** ... some are widely used
     - articles
     - data 
     - even software artefacts!
 #+BEAMER: \pause
 *** We can get no satisfaction
     \hfill of all the key criteria
 #+BEAMER: \pause
 *** 
     \hfill we adopted something radically different \hfill
 ** Intrinsic identifiers in Software Heritage
    # R. C. Merkle, A digital signature based on a conventional encryption
    # function, Crypto '87
    #+BEAMER: \vspace{-3mm}
 ***** Merkle tree (R. C. Merkle, Crypto 1979)                    :B_picblock:
       :PROPERTIES:
       :BEAMER_opt: pic=merkle, leftpic=true, width=.5\linewidth
       :BEAMER_env: picblock
       :BEAMER_act:
       :END:
       Combination of 
        - tree
        - hash function
 ***** Classical cryptographic construction
       fast, parallel signature of large data structures, built-in deduplication
 #+BEAMER: \pause
       - satisfies all three criteria
       - widely used in industry (e.g., Git, nix, blockchains, IPFS, ...)
 ** Back to basics: DIOs vs. IDOs
 *** DIO (digital identifier of an object)
     - digital identifiers for traditional (non digital) objects
       - epistemic complications (manifestations, versions, locations, etc.)
       - significant governance issues, ...
 #+BEAMER: \pause
 *** IDO (identifier of a digital object)
     - (digital) identifier for digital objects
       - much simpler to build/handle
       - can (and must) be intrinsic
 #+BEAMER: \pause
 *** Separation of concerns
     - yes, we \alert{need both} DIOs and IDOs
     - no, we \alert{must not mistake} DIOs for IDOs (and viceversa)
 ** Working together
 *** Example: links to /software source code/ in an article
     Leveraging the Software Heritage universal archive:
-    - set of files :: \small\url{swh:1:rev:06741c8c37c5a384083082b99f4c5ad94cd0cd1f}\\
-      id of tree object listing all the files in a project (at a given time)
-    - revision :: \url{swh:1:rev:7598fb94d59178d65bd8d2892c19356290f5d4e3}\\
-      id of commit object which a tree and (a pointer to) the history
-    #+BEAMER: \vspace{-2mm}\pause
-    - metadata :: this /will/ involve some form of DIO
-      - and we get all the complications back
-    #+BEAMER: \vspace{-2mm}\pause
+    - set of files :: \small\url{swh:1:dir:06741c8c37c5a384083082b99f4c5ad94cd0cd1f}\\
+		      \normalsize
+		      id of tree object listing all the files in a project (at a given time)
+    #+BEAMER: \pause
+    - revision :: \small\url{swh:1:rev:7598fb94d59178d65bd8d2892c19356290f5d4e3}\\
+		  \normalsize
+		  id of commit object which a tree and (a pointer to) the history
+    #+BEAMER: \pause
+    - metadata :: this /will/ involve some form of DIO (and we get all the
+                  complications back)
+    #+BEAMER: \pause
 *** Come in, we're open
     http://www.softwareheritage.org
     #+INCLUDE: "../../common/modules/biblio.org::#ipres2017" :only-contents t
 * A look at the internals                                        :B_appendix:
   :PROPERTIES:
   :BEAMER_env: appendix
   :END:
   #+INCLUDE: "../../common/modules/status-extended.org::#merkledemo" :minlevel 2