$$p\rightarrow q$$ $$\neg p$$ $$\overline{\therefore \neg q}$$  We were given a task to prove the validity of this argument (assuming the statement above is the same as: $(p \rightarrow q) \wedge \neg p \Rightarrow \neg q$).  I concluded with the argument to be valid. If $q$ is $0$, then the conclusion is $1$. For $p \rightarrow q$ to be true, then $p$ has to be $0$. Then $\neg p$ is $1$. This makes LHS and RHS to be $1$. Did I understand this correctly, or am I mistaken?
(p → q) ∧ ¬p ⇒ ¬q  I have tried to use the rules of inference in many ways to prove this argument to be valid. However, I cannot seem to find a way to validate the argument, but I am afraid I have missed something.  Using a truth table I find that when p and q is 0, then p → q is 1, ¬p is 1 and ¬q is 1. Would that not make the argument valid?  I apologize in advance if I have misunderstood the whole concept. Any answer would be much appreciated. Thank you
Password Protect QGIS project On a shared computer, I have a QGIS project which links up to a PostGIS database that contains my data. If a user wants to access layers from the db, they have to enter the db credentials, so that's OK.   However, I have previously logged on and imported layers from my db into QGIS, and manipulated them in QGIS (styling options based on meta-data, etc.)... Anybody who opens my QGIS project can view these layers in QGIS, and can therefore see the data I wish to be protected in my db.  Is there a way to password protect my QGIS project? How to add Android Studio to the launcher? What is the difference between private and protected members of C++ classes? What is the difference between private and protected members in C++ classes? I understand from best practice conventions that variables and functions which are not called outside the class should be made private—but looking at my MFC project, MFC seems to favor protected. What's the difference and which should I use? I want to uninstall VMware Player on my Ubuntu 12.04 LTS system. How should I uninstall it? What is the value of the series   $\sum\limits_{n=1}^\infty {\frac{1}{10^n-1}}$   and can one find closed forms for the sums   $\sum\limits_{n=1}^N {\frac{1}{10^n-1}}$?   I found that $\sum_{n=1}^N {\frac{1}{10^n-1}} $  =  $\sum_{n=1}^N (\lim_{m\to\infty  }{\frac{10^{-n}-10^{-nm}}{1-10^{-n}}})$  =  $0.111\ldots+0.0101\ldots+\ldots$ but I can't go farther.     The original question is: "Where does the second '1' appear?" Why haven't I received the "Curious" badge? As you can see in the picture, I have 13 out of 5. But it's been like this for about two months! What's the reason for that? 'as compared to' vs 'as compare to' What is the capacity of this circuit? I simply can't figure out what the capacity of this circuit is.  I can do the math myself, I just need a hint how to create an equivalent circuit where it is obvious what is parallel and what is in series... How do I vertically center a single cell within a table? ceiling fan from a switch with only black and red wires? The current switch controls an outlet in the corner of the room for a lamp. I pulled it out and noticed three sets of individual wires: two set of wires coming up into the box from the bottom, and one set with a red wire coming down into box.  All the white and grounding wires are capped.  Also all the black wires are capped; one set I’m assuming is the hot since I see it contains a red wire. On the back of the switch, the top two ports have black wires and the bottom right has the one red wire.  There are two black pigtail wires coming off the black capped wires. I tried to connect a separate switch to control a ceiling fan with remote. I ran new wire making the old switch box into a two switch. I ran 14/2 gauge wire to ceiling for fan / light remote combo. Fan didn’t work after multiple re-wiring  combinations. The breaker did pop and half click when it popped. Then I thought to re-wire the ceiling fan wires as if I was going to make it into outlet only and use a tester to indicate an open ground, or a wiring error but the two light on tester are both orange indicating correct wiring. I heard that sometimes the ceiling fan remote transformer goes bad. Should I check batteries and/or unit placement? I’m really confused at this point why the light is not working at least with remote after follow wiring installation instructions that were included with the fan. I think it’s my wiring with the switch. The way I left the wiring is that it has constant power. As if we’re a outlet the current switch does not turn it off. How to remove selected commit log entries from a Git repository while keeping their changes? I would like to remove selected commit log entries from a linear commit tree, so that the entries do not show in the commit log.  My commit tree looks something like:  R--A--B--C--D--E--HEAD   I would like to remove the B and C entries so that they do not show in the commit log, but changes from A to D should be preserved. Maybe by introducing a single commit, so that B and C become BC and the tree looks like.  R--A--BC--D--E--HEAD   Or, ideally, after A comes D directly. D' representing changes from A to B, B to C and C to D.  R--A--D'--E--HEAD   Is this possible? if yes, how?  This is a fairly new project so has no branches as of now, hence no merges as well. Terminating Python scripts in Processing framework I'm writing a Python script to use it in Processing framework. I need to cancel script execution if certain conditions are met (to save user's time). I tried to use sys.exit(arguments) command. The issue is that not only the script, but QGIS itself shuts down too. I also tried quit() but result is the same. How should I terminate script in Processing framework? The following code is for reproduction purpose only. I don't need ad hoc solution for this particular case because I already have it. I need to know how to deal with this issue in general. ##Raster processing=group ##raster_1=raster ##raster_2=raster   from osgeo import gdal import sys from numpy import * import ntpath import re import platform from PyQt4 import QtGui   raster_1 = gdal.Open(raster_1) raster_2 = gdal.Open(raster_2)  rasters_list = [raster_1, raster_2]  # create a message for the case when CRSs of rasters do not match class WrongCRS(QtGui.QMessageBox):    def __init__(self):     super(WrongCRS, self).__init__()      self.initUI()    def initUI(self):      self.warning(self, 'Oops!',             &quot;Rasters must have the same CRS!\n\nExecution cancelled!&quot;, QtGui.QMessageBox.Ok)  # check CRS proj = None for raster in rasters_list:   new_proj = raster.GetProjection()   if proj is None:     proj = new_proj   else:     if proj != new_proj:       WrongCRS()       sys.exit('CRSs do not match!')     else:       continue Best way to list files in Java, sorted by Date Modified? I want to get a list of files in a directory, but I want to sort it such that the oldest files are first.  My solution was to call File.listFiles and just resort the list based on File.lastModified, but I was wondering if there was a better way.  Edit: My current solution, as suggested, is to use an anonymous Comparator:  File[] files = directory.listFiles();  Arrays.sort(files, new Comparator&lt;File&gt;(){     public int compare(File f1, File f2)     {         return Long.valueOf(f1.lastModified()).compareTo(f2.lastModified());     } }); About 'start' and 'begin' Are 'begin' and 'start' interchangeable? Both &quot;This is a new start&quot; and &quot;This is a new beginning&quot; work, right? Then during games, they say &quot;Let's start&quot;, but I never heard &quot;Let's begin&quot;. So is there supposed to be a difference? And then one guy said this &quot;They could not begin to start a conversation&quot;. What is this supposed to mean? Is it correct? I am interested in publishing a GML file as a WFS. I don't want to use a database like PostgreSQL. What would be the rough steps I need to do for that? I like to use open source software (geoserver). I don't have much experience. I am just looking for a rough guide what kind of software I should look into and which step follows which step.. Is there a way to view your own progress towards certain badges? For example:   Tumbleweed - What value constitutes low views for a week? Fanatic  – Is there a way to view how many days in a row you currently have? Beta – Is it even possible to get this badge anymore? Does Wolfram Mathworld make a mistake describing a discrete probability distribution with a probability density function? My two main questions:  Are all URLs that include your User Id tracked?  Can the visitors who use the tracked URLs have Stack Exchange accounts?   Specifically: Recently the ability to earn badges for sharing links to posts on Stack Exchange sites . I'd like to know when and how this tracking works. It's clear that if you go to a question, and make use of the link button, you will get a URL with your User ID that will be tracked if a visitor uses it to get to SO. For example, let's use  as an example. It's regular URL is:  https://stackoverflow.com/questions/309300/defend-php-convince-me-it-isnt-horrible  If you go to that page and use &quot;save link as&quot; in the link section of the question you will be given a tracked url with your User ID:  https://stackoverflow.com/q/309300/[USER ID]  My question is, are there other URLs that would be tracked? All of the following URLs take you to the Question / Answer, but are they tracked? For example what if I just tack my User ID onto the long url?  https://stackoverflow.com/questions/309300/defend-php-convince-me-it-isnt-horrible/[USER ID]  What if I add my User ID to an answer URL?  https://stackoverflow.com/questions/309300/defend-php-convince-me-it-isnt-horrible/309622#309622/[USER ID]  or even  https://stackoverflow.com/q/309622/[USER ID]   Is there a way to know that a URL is being tracked? Is there some sort of format to follow? Are the only tracked URLs the ones provided in the Question links? Finally, does this sentence from the blog post mean that visitors cannot have an account?  Also, the tracked IPs must originate from outside our existing network. Proving an inclusion related to algebraic sets and interpreting it I don't think this has yet been covered in .  There was , however, it was not specifically talking about the case where the proper noun ends in a plural noun.  Feel free to vote to close if I am wrong.  What is the correct way to make a proper noun ending in a plural noun ending in an "s" possessive?  This frequently happens with corporations, e.g., "Dunkin' Donuts."  Should one work off of the fact that the entity is singular—suggesting Dunkin' Donuts's—or should one work off of the fact that "Donuts" is plural and ending in an "s"—suggesting Dunkin' Donuts'?  I expect that the answer might depend on dialect because some regions refer to corporations in the singular form ("Dunkin' Donuts is a company") while other regions refer to corporations in the plural form ("Dunkin' Donuts are a company").  I am specifically interested in American English, but would be interested in hearing answers for other dialects too.