tikz drawing layers?
"Z-level" in TikZ
What is this rhetorical scheme or literary device called? I can't recall the name of the rhetorical scheme or literary device involved with using the same word more than once within the same sentence but with different meanings:  "The only thing we have to fear is fear itself."    fear - verb fear - noun   "Turn right right here."   right - adv. directional right - adv. in this place   "My feet are but feet away."   feet - noun lower appendage feet - noun distance I've been trying to play with a rigid body simulations.  I prepared a project of a building made of domino tails. I've placed all objects very tight, but as soon as I start animation it looks like there was some tiny gap between objects, so they all fall down a little bit. For a high building it leads to a construction disaster as the whole building colapses.  Here is an example:  (I'd suggest to use 0.25x speed).  How can I fix it? I have run into an issue with WPF and Commands that are bound to a Button inside the DataTemplate of an ItemsControl. The scenario is quite straight forward. The ItemsControl is bound to a list of objects, and I want to be able to remove each object in the list by clicking a Button. The Button executes a Command, and the Command takes care of the deletion. The CommandParameter is bound to the Object I want to delete. That way I know what the user clicked. A user should only be able to delete their "own" objects - so I need to do some checks in the "CanExecute" call of the Command to verify that the user has the right permissions.  The problem is that the parameter passed to CanExecute is NULL the first time it's called - so I can't run the logic to enable/disable the command. However, if I make it allways enabled, and then click the button to execute the command, the CommandParameter is passed in correctly. So that means that the binding against the CommandParameter is working.  The XAML for the ItemsControl and the DataTemplate looks like this:  &lt;ItemsControl      x:Name="commentsList"     ItemsSource="{Binding Path=SharedDataItemPM.Comments}"     Width="Auto" Height="Auto"&gt;     &lt;ItemsControl.ItemTemplate&gt;         &lt;DataTemplate&gt;             &lt;StackPanel Orientation="Horizontal"&gt;                 &lt;Button                                                  Content="Delete"                     FontSize="10"                     Command="{Binding Path=DataContext.DeleteCommentCommand, ElementName=commentsList}"                      CommandParameter="{Binding}" /&gt;             &lt;/StackPanel&gt;                                 &lt;/DataTemplate&gt;     &lt;/ItemsControl.ItemTemplate&gt; &lt;/ItemsControl&gt;   So as you can see I have a list of Comments objects. I want the CommandParameter of the DeleteCommentCommand to be bound to the Command object.  So I guess my question is: have anyone experienced this problem before? CanExecute gets called on my Command, but the parameter is always NULL the first time - why is that?  Update: I was able to narrow the problem down a little. I added an empty Debug ValueConverter so that I could output a message when the CommandParameter is data bound. Turns out the problem is that the CanExecute method is executed before the CommandParameter is bound to the button. I have tried to set the CommandParameter before the Command (like suggested) - but it still doesn't work. Any tips on how to control it.  Update2: Is there any way to detect when the binding is "done", so that I can force re-evaluation of the command? Also - is it a problem that I have multiple Buttons (one for each item in the ItemsControl) that bind to the same instance of a Command-object?  Update3: I have uploaded a reproduction of the bug to my SkyDrive: Python module for converting PDF to text Is there any python module to convert PDF files into text? I tried  found in Activestate which uses pypdf but the text generated had no space between and was of no use. I've managed to create a custom keyboard layout for .  Now that the keyboard is in a state that I can share it. I don't know how to make it a redistributable package. Suppose we have a sample of size n= 9, where the sum equals 27, and the sum of the squaredvalues equals 113. Sample mean is 27/9=3 and mean of squared values is 113/9 = 12.56 Can we then say that the sample variance $S^2 = E(\overline X^2) - E(\overline X)^2 = 12.55 - 9 = 3.56$ ? Which tables are safe to clear? Find the number of dissimilar terms in the expansion of $$\bigg(x+\frac{1}{x}+x^2+\frac{1}{x^2} \bigg)^{20}$$  Could someone give me some hint to proceed in this question. I used $x+1/x=t$ and wrote expansion as $(t^2+t-2)^{20}$ but even this does not convey much information. Please help. "E:Read error - read (5: Input/output error), E:The package lists or status file could not be parsed or opened." So I keep trying to install things on my laptop and whenever I try to use sudo apt-get I get the same errors every  time,  SystemError: E:Read error - read (5: Input/output error), E:The package lists or status file could not be parsed or opened.   Also whenever I try to open software Center through my desktop Icon it will just freeze leaving me to force quit.  If I try to use the command software-center in my terminal I get the longest list in the world which is,   che.open() Traceback (most recent call last):   File "/usr/lib/python2.7/dist-packages/gi/overrides/GLib.py", line 629, in &lt;lambda&gt;     return (lambda data: callback(*data), user_data)   File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 261, in open     self._cache = apt.Cache(progress)   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 105, in __init__     self.open(progress)   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 150, in open     self._cache = apt_pkg.Cache(progress) SystemError: E:Read error - read (5: Input/output error), E:The package lists or status file could not be parsed or opened. 2013-10-13 10:13:52,685 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open() Traceback (most recent call last):   File "/usr/lib/python2.7/dist-packages/gi/overrides/GLib.py", line 629, in &lt;lambda&gt;     return (lambda data: callback(*data), user_data)   File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 261, in open     self._cache = apt.Cache(progress)   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 105, in __init__     self.open(progress)   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 150, in open     self._cache = apt_pkg.Cache(progress) SystemError: E:Read error - read (5: Input/output error), E:The package lists or status file could not be parsed or opened. 2013-10-13 10:13:57,365 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open() Traceback (most recent call last):   File "/usr/lib/python2.7/dist-packages/gi/overrides/GLib.py", line 629, in &lt;lambda&gt;     return (lambda data: callback(*data), user_data)   File "/usr/share/software-center/softwarecenter/db/pkginfo_impl/aptcache.py", line 261, in open     self._cache = apt.Cache(progress)   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 105, in __init__     self.open(progress)   File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 150, in open     self._cache = apt_pkg.Cache(progress) SystemError: E:Read error - read (5: Input/output error), E:The package lists or status file could not be parsed or opened.   That's only about one-tenth of the list which is too long to read. I need help, if anyone has an answer please respond Javascript variables keep track to their copies? How many people can the TARDIS transport? The interior of a TARDIS is much larger than its exterior, but how many occupants can it transport? What is the purpose of wrapping whole Javascript files in anonymous functions like “(function(){ … })()”? calculating expected number of packets. How to Calculate the time of Charging and Discharging of battery? Compare means of group with a mean of a subgroup How can I add the Memtest86+ options back to the Grub menu? The app forgets that I voted when I scroll the question I want to hit enemy's axe to break it. How this is properly played in D&amp;D 5e? And what about shield or armor? Can I attack these items to break it? I will be traveling from Australia to Austria, transferring in Abu Dhabi. Is it alright for me to bring a vibrator in the check-in luggage, or are there laws against that?  It is approximately 17cm long. Are there any precautions to take? Confidence interval interpretation in linear regression when errors are not normally distributed