I was writing an essay on The Cow. I started like this:  The cow is a four-footed domestic animal. It has a big body...   ....There are many different breeds of cows in the world.  You would notice that I started with 'the cow' and then I changed to 'cows'. Is there anything wrong about this? Is it grammatically incorrect switching between them two?
When speaking precisely or technically, one would say that "Homo erectus and homo sapiens are two species of hominid" rather than "Homo erectus and homo sapiens are two species of hominids." The hominid here should be singular because we are speaking about instances of a single class ("class" being used here in its broader sense, not in the sense of taxonomic grouping).  Now let's consider more common parallel constructions replacing the word species with other words.      Tide and Wisk are two brands of detergent.       Tide and Wisk are two brands of detergents.      Cats and dogs are two types of pet you can buy at Pets-R-Us.       Cats and dogs are two types of pets you can buy at Pets-R-Us.   I feel that using the singular noun to specify the class is more grammatically correct, but sounds stilted in conversation. Almost everyone I hear making these constructions uses the plural form. What are your thoughts about singular vs. plural here?  Edit  Here's a more extreme example that may help clarify the issue. Consider the following sentence:     It was my first attempt at calming an angry crowd, and I just        stood there while people were hurling all kinds of insults at me.   Here I think the singular insult sounds strange, if not downright wrong.  Further Edit  I just noticed in A Treasury for Word Lovers (Morton S. Freeman, 1983) a section entitled "Types of Errors." This is a book about (American) English usage by an English professor and editor, which purports to be a "practical guide for serious writers and readers." I wish I could say this discovery satisfies the question, but in fact I now feel somewhat farther from the truth, if there is any single "truth" in this matter. But at least I don't have to worry about being wrong when using the plural form of the class in these constructions.
Now that  is in effect, people who have visited Iraq, Syria, Iran, or Sudan since 2011 are banned from entering the US under the Visa Waiver Program. However it's unclear to me how could the US officials prove one has set foot in those countries, unless:   There's a stamp in one's passport indicating so, which can be side-stepped by getting a fresh passport One mentions the fact on the ESTA application form, which is obviously easy to avoid   Is there any other way the US might be able to identify such individuals?  NB: I'm not eligible for the VWP myself and don't plan to travel to the four countries above, so it's a purely theorethical question I'm working through a problem regarding expected values in Markov chains, and at some point it says:     Recall from probability that if $X$ is a positive integer valued random variable, then $\mathbb{E}[X] = 1 + \sum^\infty_{k=1}\mathbb{P}(X &gt; k)$.   I know that by definition $\mathbb{E}[X] = \sum_a a\mathbb{P}(X = a)$, but I can't see how the above equality follows from this, nor am I sure if this is how to approach the problem. Switching between one and two monitors When running my MBP, I attach an external monitor, a keyboard and trackpad to it so I have two separate desktops which are contiguous; like it's a "fancy" desktop.   Back in the day on Mavericks, it behaved properly: when I unplugged the external monitor to, say, take the laptop into a meeting, it would just put all of the desktops separately on the built in display, roughly preserving which window stayed on which desktop so all you'd have to use was a run a restore tool like Display Maid to restore your window positions when you plug your external monitor back in. This was handy because you didn't have to manually clean up your desktop when done.   Now, with El Cap, it would seem that when you unplug the external monitor, it used the monitor count of whichever screen had the most desktops and merges the windows from the two "combined desktops" into one desktop in a way that seemed to be random, which is clumsy.   Worse, setting back Display Maid to restore the original configuration automatic doesn't work like it used to - previously it saved positions on all desktops in one action, but now it does it one screen at a time and forcing you restore eech desktop separately, which is tedious. It would seem that Display Maid is not great software anymore.  Is there some other utility out there that must work better so you can restore how your windows and desktop setup was as it was before you unplugged the external monitor. Any ideas? Ubuntu 14.04: very slow UI in Oracle VirtualBox Short summary: 14.04 is much slower than 12.04 even with more RAM assigned.  I'm using latest VirtualBox 4.3.10 on Mavericks 10.9.2. How can I make it faster? How can I produce a 'ring (or wheel) chart' like that on page 88 of the PGF manual? Sending signals to USB port using C I want to send a simple 5V signal to the usb port. The USB cabel's insulation will be removed and connected to a relay which is connected to an electric door system. I think I should write this code in C. Can somebody give me a hint? What is a plain English explanation of "Big O" notation? I'd prefer as little formal definition as possible and simple mathematics. Word caption style -- different style for label and number? This should be a common problem for anyone involved in technical writing.  When you insert an image (or table etc.) caption in Word, you get  dialog. You enter your caption,  "A happy bicycle" (in yellow).  This might be fine for a happy bicycle, but I want to have captions that have one style for the "enumeration" (label and number) and one style for the description (caption text, as called by Word), as such:    I have tried searching for this but I haven't found anything yet... Tracing a monochrome image into a 3D, extruded object with a script Send mail without MFMailComposeViewController Splicing a Javascript array from within the callback passed to forEach I have a configuration file where a developer can specify a text color by passing in a string:   &lt;text value="Hello, World" color="Red"/&gt;   Rather than have a gigantic switch statement look for all of the possible colors, it'd be nice to just use the properties in the class System.Drawing.Brushes instead so internally I can say something like:   Brush color = Brushes.Black;   // Default   // later on...  this.color = (Brush)Enum.Parse(typeof(Brush), prasedValue("color"));   Except that the values in Brush/Brushes aren't enums.  So Enum.Parse gives me no joy.  Suggestions? Using File Geodatabase coded domain with ArcGIS Online? I created a File GDB and set up a domain, and the domain was assigned to a field in a feature class. The domain behaves as expected on ArcGIS Desktop (dropdown list when editing the content of that field).  But if I zip up the FGDB and upload to ArcGIS Online to created a feature layer and edit the layer online, there is no dropdown when editing.  I don't see any additional step in this tutorial, other than a different mechanism of getting data to ArcGIS Online. I don't think I can do it the same way in ArcGIS 10.0:   Anyone has any idea what's going on? Evaluate $\lim_{n\to\infty} [{1\over kn}+{1\over k(n+1)}+{1\over k(n+2)}+\cdots+{1\over k(n+p-k)}]$ where $k<p$ There are four options. Which of them is correct?- (a)${p\over k}$ (b)${k\over p}$ (c)$\log({p\over k})$ (d)${\log p\over k}$ I somehow want to use the rule for evaluating this kind of sum using integration, i.e. $\int_{0}^{1} f(x) \ dx=\lim_{n\to\infty} {1\over n}\sum_{r=1}^{n}f({r\over n})$  But the given expression $\lim_{n\to\infty} [{1\over kn}+{1\over k(n+1)}+{1\over k(n+2)}+\cdots+{1\over k(n+p-k)}]={1\over k}\lim_{n\to\infty}{1\over n}\sum_{r=0}^{p-k}\frac{1}{1+{r\over n}}$, sum running from $0$ to $p-k$ instead of $n$. So, how to evaluate this limit? Thanks for assistance in advance. How to get Intel Dual Band Wireless-AC 3168 work on Ubuntu 16.04? Are moving objects producing stronger gravity fields? If the strength of gravitational influence exerted by a body is derived from its mass and energy then is it true that a moving object which has some kinetic energy should also produce stronger gravitational pull than a static/slower one?  If that's correct then would it be also possible for an object moving fast enough to produce gravity so strong that it would collapse into a (fast moving) black hole? \bordermatrix with brackets [ ] instead of parentheses ( ) I have the following code:  \documentclass{article} \begin{document} $ M = \bordermatrix{~ &amp; x &amp; y \cr               A &amp; 1 &amp; 0 \cr               B &amp; 0 &amp; 1 \cr} $ \end{document}   But this code makes a matrix with () and i would like it to be with [] How do i do this? I would like to change the caption in the List of Tables in a way it is different from the caption in the corresponding table. How can I do that? Does there exist a command to do that? How to sum up values of each two rows across their line in linux $S^2 \times S^2$ is diffeomophic to $G_2(\mathbb{R}^4)$ $G_2(\mathbb{R}^4)$ is the Grassmannian manifold of two-dimensional subspaces of $\mathbb{R}^4$. I would like a detailed proof. Can it be done explicitly? I mean, showing the map and checking its differentiability using charts?