Is the fabric of space time a real thing?
If the universe is 3D, how is space-time like a "fabric"?
I have a Python function that takes a numeric argument that must be an integer in order for it behave correctly. What is the preferred way of verifying this in Python?  My first reaction is to do something like this:  def isInteger(n):     return int(n) == n   But I can't help thinking that this is 1) expensive 2) ugly and 3) subject to the tender mercies of machine epsilon.   Does Python provide any native means of type checking variables? Or is this considered to be a violation of the language's dynamically typed design?  EDIT: since a number of people have asked - the application in question works with IPv4 prefixes, sourcing data from flat text files. If any input is parsed into a float, that record should be viewed as malformed and ignored. I know that there are questions asking like "intersection of a infinite collection of sets" and I can understand that the answer for that one is a null set, but I got a question here, in which all sets are finite and nonempty. Please take a look at the pic below.  It's a True/False question.  What I'm confused about is that the "infinity" sign in the interception. Since all sets are finite, does it mean that there are many sets in the chain are the same? (because the symbol used is for subsets not for proper subsets). Please give me some hints how I should think about this question.  Thank you My 3-month-old son has started sleeping through the night, with a vengeance. He sleeps for hours. And when he finally wakes up and I expect him to be starving, he's often still ready to happily play for a bit - say 1/2 hour to 45 min. Now, I know this isn't such normal behavior for a 3-month-old, and I'm definitely appreciating having my nights back, but I'm also a bit concerned - how long is the longest I should let him go without eating?  Edit (more details):  I used to try to stretch him and make his last feeding right before I went to sleep, so that I could take full advantage of his sleep-time. So we used to put him to bed about 12:30-1:00, and then head to sleep ourselves. He started off going about 6-7 hours... But a couple of weeks ago he started sleeping longer, and longer, and longer... Now he goes nearly 12 hours. He'll go to sleep at 12:30 AM and wake up at 12 PM or later. And he'll then happily play for another half hour, making about 12 hours of no-eating. I generally trust that I can rely on him to tell me when he's hungry, but I was wondering if there's a limit to how long I can let him go without eating... Prove that $f$ has a fixed point . If we look at light as a collection of little particles, we can say that dimmer light has its photons more spread out.  But if we look at light as a wave, then there no gaps unless specifically placed there on purpose.  So how can one interpret the formation of gaps between the photons? Composition of two Riemann integrable functions Suppose $f,g$ are two Riemann  Integrable functions .Is it true that $f\circ g$ is also Riemann  Integrable?  Trying this for a long time but not getting the answer Is there any IC that interfaces any 3.3V Input/Output to 5V Output/Input? I need it primarily for an Arduino Due but if there any bidirectional IC that works like that it would be great.  Some people advised me to use the SN74AHC125 and CD4050 ICs, but I don't understand how they work or how to interface with them. I have a database with millions of phone numbers with free-for-all formatting. Ie, the UI does not enforce any constraints and the users are typing in whatever they want.  What I'm looking for is a Java API that can make a best-effort to convert these into a consistent format. Ideally, the API would take the free text value and a country code and produce a valid international phone number or throw an exception.  For example, a phone number in the system might look like any of the following:  (555) 478-1123 555-478-1123     555.478.1123 5554781123   Given the country of US, the API would produce the value "+1 (555) 478-1123" for all these. The exact format does not matter, as long as it's consistent.  There are also numbers in the system without area codes, such as "478-1123". In that case, I would expect a NoAreaCodeException, or something similar.  There could also be data such as "abc", which should also throw exceptions.  Of course, there are countless variations of the examples I have posted, as well as the enormous complication of international phone numbers, which have quite complicated validation rules. This is why I would not consider rolling my own.  Has anyone seen such an API? I have a query to insert a row into a table, which has a field called ID, which is populated using an AUTO_INCREMENT on the column. I need to get this value for the next bit of functionality, but when I run the following, it always returns 0 even though the actual value is not 0:  MySqlCommand comm = connect.CreateCommand(); comm.CommandText = insertInvoice; comm.CommandText += "\'" + invoiceDate.ToString("yyyy:MM:dd hh:mm:ss") + "\', " + bookFee + ", " + adminFee + ", " + totalFee + ", " + customerID +  ")"; int id = Convert.ToInt32(comm.ExecuteScalar());   According to my understanding, this should return the ID column, but it just returns 0 every time. Any ideas?  EDIT:  When I run:  "INSERT INTO INVOICE (INVOICE_DATE, BOOK_FEE, ADMIN_FEE, TOTAL_FEE, CUSTOMER_ID) VALUES ('2009:01:01 10:21:12', 50, 7, 57, 2134);last_insert_id();"   I get:  {"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'last_insert_id()' at line 1"} Do fixtures trigger model callbacks? I am taking an abstract algebra course and I am really interested about the topic.  So much so that I spend most of my time reading supplementary materials.  I consequently know a lot more theorems than the ones covered in class.    In a recent quiz, I used a theorem in one of my proofs that was not mentioned in the lecture since.  My professor gave me partial marks for my answer for the reason that we didn't cover this theorem in class even though the proof was completely valid!  I can't really see where he is coming from.  How would someone be able to use a theorem correctly if he doesn't know its proof?  I was quite baffled by his comment.   Do you agree with this?  EDIT: The professor just Emailed me and said that after thinking for a while, he decided to award me the full mark for the question. He also mentioned that he didn't want discourage me from studying the subject (since he saw most of my previous quiz grades were full marks) and I was passionate about it, but kindly requested that I include any proof for a theorem that I cite from now on in his exams. He also sent a broadcast message to the whole class indicating this. Difference between if () { } and if () : endif; Are there any differences between...  if ($value) {  }   ...and...  if ($value):  endif;   ? A specific file on our production servers is being modified at apparently random times which do not appear to correlate with any log activity.  We can't figure out what program is doing it, and there are many suspects.  How can I find the culprit?  It is always the same file, at the same path, but on different servers and at different times.  The boxes are managed by , but the puppet logs show no activity at the time the file is modified.  What kernel hook, tool, or technique could help us find what process is modifying this file?    lsof is unsuitible for this, because the file is being opened, modified and closed very quickly.  Any solution that relies upon polling (such as running lsof often) is no good.      OS: Debian testing Kernels: Linux, 2.6.32 through 3.9, both 32 and 64-bit. Hiding the sidebar in Ubuntu I have two questions :  First, I wanted to hide Ubuntu’s side-bar, so I set the settings in appearance to 'autohide'. The side bar did indeed disappear but when I roll over the left side, the side bar don't appear again. So, I am using a virtual box. Can it explain the fact that this bar doesn't show again when it is set to autohide.   Second, assuming I wouldn't be able to come over the problem, I pined to the dock every element of the sidebar, except the dash home. Is it possible either to pin it in the dock or to launch it from the terminal ? Lost/Deleted dpkg (package manager for Debian). How do I get it back? Environments are allowed to have arguments, but reference to those arguments can only appear in the opening code of the environment, and not the closing code.  What is the reason for this, and are there preferred ways around it?  e.g.  \newenvironment{foo}[1]% {some code #1} % allowed {some code #1} % not allowed How to type a circumflex over a greek letter in text mode? Short story with competitors complaining to government about a new very popular synthetic food IE must close for event with jQuery to work When $z\neq 0$, $\arg z$ is defined to be the set $\{\theta \in \mathbb{R} : z=|z|e^{i\theta}\}$.  What if $z=0$? Usually does one leave the argument of $0$ undefined? Or is $\arg 0 = \mathbb{R}$?