@@ -1,24 +1,24 @@
 /*
 # map
 
-    http://www.cplusplus.com/reference/map/map/
+http://www.cplusplus.com/reference/map/map/
 
-    Also comes in an unordered version `unordered_map`.
+Also comes in an unordered version `unordered_map`.
 
-    Ordered.
+Ordered.
 
-    Also comes in an multiple value input version `multimap`.
+Also comes in an multiple value input version `multimap`.
 
-    Does not require a hash function. Usually implemented as a self balancing tree such as a rb tree.
+Does not require a hash function. Usually implemented as a self balancing tree such as a rb tree.
 
 # hashmap
 
-    There seems to be no explicit hashmap container, only a generic map interface,
+There seems to be no explicit hashmap container, only a generic map interface,
 
-    However unordered_map is likely to be hashmap based.
+However unordered_map is likely to be hashmap based.
 
-    A nonstandard `hash_map` already provided with gcc and msvc++.
-    It is placed in the `std::` namespace, but it is *not* ISO.
+A nonstandard `hash_map` already provided with gcc and msvc++.
+It is placed in the `std::` namespace, but it is *not* ISO.
 */
 
 #include "common.hpp"
@@ -76,7 +76,7 @@ int main() {
     }
 
     /*
-    emplace
+    # emplace
 
         Put a value pair into the map without creating the pair explicitly.
 
 
@@ -1,14 +1,14 @@
 /*
 # set
 
-    -   unique elements: inserting twice does nothing
+Implemented with Red Black trees in GCC 6.4:
+https://stackoverflow.com/questions/2558153/what-is-the-underlying-data-structure-of-a-stl-set-in-c/51944661#51944661
 
-    -   always ordered: $O(log)$ find / insert
+A hashtable would be unlikely because it is sorted and can be efficiently iterated.
 
-    -   immutable elements: it is not possible to modify an object,
-        one must first remove it and resinsert.
+Unique elements: inserting twice does nothing.
 
-        This is so because modification may mean reordering.
+Immutable elements: it is not possible to modify an object, one must first remove it and resinsert. This is so because modification may mean reordering.
 */
 
 #include "common.hpp"
@@ -81,7 +81,7 @@ int main() {
     /*
     # insert
 
-        Return is a pair conatining:
+        Return is a pair containing:
 
         - if the item was not present, an iterator to the item inserted and true
         - if the item was     present, an iterator to the existing item inserted and false
 
@@ -4,35 +4,36 @@ How to build GCC from source.
 
 Tested with: version 5.1.0 on Ubuntu 14.04 in a 2013 computer.
 
-Summary:
+Summary local build:
 
     sudo apt-get build-dep gcc
     # Required to compile gnat.
     sudo apt-get install gnat-4.8
-    mkdir gcc
+    git clone git://gcc.gnu.org/git/gcc.git
     cd gcc
-    git clone git://gcc.gnu.org/git/gcc.git src
-    cd src
     # No annotated tags... so no describe.
     git checkout gcc-5_1_0-release
     ./contrib/download_prerequisites
-    cd ..
     mkdir build
     cd build
     # C and C++ only.
-    ../src/configure --enable-languages=c,c++ --prefix="$(pwd)/../install"
+    ../configure --enable-languages=c,c++ --prefix="$(pwd)/install"
     # Add a suffix to the executable names:
     # --program-suffix="-4.7"
     # All languages.
-    # ../src/configure --enable-languages=all --prefix="$(pwd)/../install"
+    # ../configure --enable-languages=all --prefix="$(pwd)/install"
     # Wait hours.
-    make -j5
+    make -j$(nproc)
+
     # Wait hours.
-    make check
+    #make check
+
     # Install executables to /usr/local/bin
     # There are also many other installed files under /usr/local.
-    sudo make install
-    gcc -v
+    make install
+
+    # Use it.
+    ./install/bin/gcc -v
     # sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 60 --slave /usr/bin/g++ g++ /usr/bin/g++-4.9
 
 Or install locally for interactive testing: