When to add "the", "a" or when not to add "the" or "a"?
Are there any simple rules for choosing the definite vs. indefinite (vs. none) article?
removeGroup() in QGIS 3 I am updating a plugin from QGIS 2 to 3.  I need to iterate through the groups (the names are dynamic) and remove them with their respective child layers.  I need to get a list of groups and then iterate through the groups and delete them.  The original code is as follows:  legend = self.iface.legendInterface() group_names = legend.groups() rev = self.groups[:] rev.reverse() ...     for i, group in enumerate(rev):         legend.removeGroup(group)   I replaced self.iface.legendInterface() with QgsProject.instance().layerTreeRoot() but group_names = legend.groups() fails with the message 'QgsLayerTree' object has no attribute 'groups'   What is the proper container of the groups and how do I access the collection; and, once found, how do I delete those groups?  A search for information on how to remove groups from a layer tree in QGIS 3 has proven fruitless. How can I reuse existing materials, objects, etc from an existing .blend? I have created several designs for a particular project and they are related, but I don't want to have to keep recreating any similar elements, such as shared materials or textures.  How can I use the existing data in a new Blender file? Computing the Galois group of polynomials $x^n-a \in \mathbb{Q}[x]$ Can't update because the word prox* is blocked Why is foo.hasOwnProperty('__proto__') equal to false? What is a 'Closure'? I asked a question about Currying and closures were mentioned. What is a closure? How does it relate to currying? Float/double precision in debug/release modes Do C#/.NET floating point operations differ in precision between debug mode and release mode? How to match all occurrences of a regex A smooth vector field on $S^2$ vanishing at a single point I need to find a vector field as described in the title.  I was given a couple hints, and this is what I have so far. Let $\varphi:S^2\setminus\{N\}\to\mathbb{R}^2$ be stereographic projection ($N$ is the north pole). Let $Y$ be a smooth, non-zero vector field on $\mathbb{R}^2$ that dies off to $0$ "at infinity." Since $\varphi$ is a diffeomorphism, we can push $Y$ forward along $\varphi^{-1}$ to get a smooth vector field $(\varphi^{-1})_*Y_{\varphi(p)}$ on $S^2$. But this vector field is not zero at the north pole... it's undefined. So can I just define my vector field on $S^2$, call it Z, to be the pushforward of $Y$ (as above) away from $N$ but $0$ at $N$? And if so, do we still have smoothness? Recursive function, if and which statements delaying moldy bread I always keep bread around, home-made or otherwise.  Is there a way to keep it from molding, or at least delay the process?  I've tried the fridge with some success (extra day or two), but I don't like my bread that cold to eat.  I've tried zip-top bags with no success (seems to mold faster).  Bread-box didn't seem to make any difference in time.  Thanks I recently updated my operating system from Ubuntu 13.04 to Ubuntu 13.10. Since then, I am facing difficulties compiling my TeX code in which the french babel package is called. Please note that all my sources were compiling very fine before the system upgrade. However, now, given the following header:   \usepackage[francais]{babel}  I receive the following error:  ! Package babel Error: Unknown option `francais'. Either you misspelled it   What should I do? Please note that if I remove this part of code (\usepackage[francais]{babel}), everything is compiling well. I also tried it with french, and I receive the same result. Thank you in advance for your help.  MINIMUM WORKING EXAMPLE : \documentclass[11pt,a4paper]{article} \usepackage[utf8]{inputenc} \usepackage[francais]{babel} \usepackage[T1]{fontenc} \usepackage{amsmath} \usepackage{amsfonts} \usepackage{amssymb}  \begin{document} This is a MINIMUM WORKING EXAMPLE. \end{document}   ! Package babel Error: Unknow option `francais'. Either you misspelled it Connecting two DC wallwarts in series - to produce dual DC supply I have two 9 V, 300 mA wallwarts and would like to connect them in series to produce +9 V, 0 V and -9 V. This can be done with two 9 V batteries (as seen below), but can I do this with two non-identical wallwarts? How to render a pixelated, occluded wireframe with freestyle? I'd like to combine these features:    The pixelated look of a wire material with anti-aliasing disabled. Proper occlusion of hidden lines.   A wireframe material produces the first feature, freestyle produces the second. Can a line set be created that produces neither double pixels nor gaps? Line thickness alone does not seem to be the answer.  There is the trick with two materials and z-offset, but I have trouble getting a really clean solution at the outline of the object. So a freestyle solution would be best.    The main problem is that freestyle (to the right) produces double pixels: I am trying to calculate the following limit without Stirling's relation.  \begin{equation} \lim_{n \to \infty} \dfrac{n!}{n^n} \end{equation} I tried every trick I know but nothing works. Thank you very much. Can I kill an indestructible creature with -X/-X and sufficient damage marked on it? Can I hit a 4/4 indestructible creature with a  (3 damage) and give it -1/-1 with  to kill it? (Does it matter which way around I cast those?)  I read  here and it says, damage is removed in cleanup step, so it should be on the creature still after both spells.     702.12. Indestructible   702.12a Indestructible is a static ability.   702.12b A permanent with indestructible can’t be destroyed. Such permanents aren’t destroyed by lethal damage, and they ignore the state-based action that checks for lethal damage (see rule 704.5g).   702.12c Multiple instances of indestructible on the same permanent are redundant. Linux: clnt_create: RPC: Program not registered NFS mounts recently automatically got un-mounted. When I checked, the NFS service status it was shown to be running.  [root@hsluasrepo]# service nfs status rpc.svcgssd is stopped rpc.mountd (pid 4083) is running... nfsd (pid 4148 4147 4146 4145 4144 4143 4142 4141) is running... rpc.rquotad (pid 4079) is running...  [root@hsluasrepo]# service rpcbind status rpcbind (pid  4203) is running...  [root@hsluasrepo common]# rpcinfo -p 10.80.3.154    program vers proto   port  service     100000    4   tcp    111  portmapper     100000    3   tcp    111  portmapper     100000    2   tcp    111  portmapper     100000    4   udp    111  portmapper     100000    3   udp    111  portmapper     100000    2   udp    111  portmapper   But showmount output was showing an error.  [root@hsluasrepo ]# showmount -e 10.80.3.154 clnt_create: RPC: Program not registered   After restarting the NFS service, showmount output displayed the NFS server's export list.  Can anyone tell me the root cause of this issue and How to avoid this problem in future?  /var/log/messages:  Jul 7 03:22:01 hsluasrepo rsyslogd: [origin software="rsyslogd" swVersion="5.8.10" x-pid="1188" x-info="rsyslog.com"] rsyslogd was HUPed Jul 7 03:22:02 hsluasrepo rhsmd: In order for Subscription Manager to provide your system with updates, your system must be registered with RHN. Please enter your Red Hat login to ensure your system is up-to-date. Jul 8 03:22:01 hsluasrepo rhsmd: In order for Subscription Manager to provide your system with updates, your system must be registered with RHN. Please enter your Red Hat login to ensure your system is up-to-date. Jul 8 16:36:55 hsluasrepo kernel: nfsd: last server has exited, flushing export cache Jul 8 16:36:55 hsluasrepo rpc.mountd[4083]: Caught signal 15, un-registering and exiting. Jul 8 16:36:55 hsluasrepo rpc.mountd[24463]: Version 1.2.3 starting Jul 8 16:36:55 hsluasrepo kernel: NFSD: Using /var/lib/nfs/v4recovery as the NFSv4 state recovery directory Jul 8 16:36:55 hsluasrepo kernel: NFSD: starting 90-second grace period Jul 8 16:37:32 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.208:1004 for /common/PROD (/common/PROD) Jul 8 16:38:09 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.181:869 for /common/PROD (/common/PROD)  Jul 8 16:38:43 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.180:825 for /common/PROD (/common/PROD) Jul 8 16:39:12 hsluasrepo rpc.mountd[24463]: authenticated mount request from 10.60.5.176:688 for /common/PROD (/common/PROD) Are the following sentences grammatical or not? If not, does substituting a to-infinite make them grammatical? (Optional: designate if the sentence expresses purpose, reason, aim, or function)  1 I have decided to purchase a jet for getting to NYC and back more quickly. 2 I have decided to buy a jet for having a quicker way to get to NYC and back.  This is my only reason and aim; this will be the jet's only purpose and function.  3 I hate hairdryers, so I am buying a space heater for drying my hair more naturally, and that is my only aim &amp; purpose &amp; reason and that will be its only function 4 For having a lasting shine in your hair, buy ShineOn Shampoo. 5 My neighbor and I have decided to cooperate more for having a better life together.   Research done: ELL  (Note the  here is a restatement of Cambridge Dictionary's ) ELL  ELL  BBC English  (Currently the best site I've found.) ELU  All of which have answers that I find  (i) incomplete (ii) contradictory (iii) terribly confusing, if not (iv) wrong. To sort through the haze, I am focusing on one issue. Background Some sources say that you need to use a to-infinitive for expressing purpose, aim, function, reason, etc. I find these to be rather hazy distinctions, given that the ODO defines  as The reason for which something is done or created or for which something exists and the same work lists as : aim, reason, function, etc. It is my assertion that at least some of the following sentences demonstrate that one can use the -ing form (be it a gerund, verbal noun, participle) to express individual purpose (aim, reason, function, intention, whatever you want to call it). Do you agree, or not? Why (not)?  In shorter terms, are the sentences grammatical? or do we have to substitute a to-infinitive (including in order to + infinitive) to make them grammatical? (Optional: designate if the sentence expresses purpose, reason, aim, function, etc.) What are valid values for the id attribute in HTML? When creating the id attributes for HTML elements, what rules are there for the value? Are the square roots of all non-perfect squares irrational?