"That is me." Why is this incorrect and why should we use "that is I" please?  I think we can't say the pronoun "that" can't act as a subject:  That is a keyboard.  Who is she? Here, too, "who" is not considered as the subject apparently! Is its reason the same as above?  What makes her happy?  But here "what" is considered as a subject!  I suppose the issue related to the problem is in the use of "to be" words, in the first two sentences above.  Do you agree?  All answers and comments are warmly welcome, I also would like to see StoneyB's answer. :-)
It is me who am to blame.    It is I who am to blame.      Which one is correct here? I am bewildered about these two sentences.
Getting text from last marker to EOF in POSIX.2 I have a text with marker lines like:  aaa --- bbb --- ccc   I need to get a text from the last marker (not inclusive) to EOF. In this case it will be  ccc   Is there an elegant way within POSIX.2? Right now I use two runs: first with nl and grep for the last occurrence with respective line number. Then I extract the line number and use sed to extract the chunk in question.  The text segments may be quite large, so I'm afraid to use some text-adding method like we add the text to a buffer, if we encounter the marker we empty the buffer, so that at EOF we have our last chunk in the buffer. I've just begun to work learn Linear Algebra on my own through Hoffman and Kunze's book and the first problem set already has a question that I can't solve:  Prove that if two homogeneous systems of linear equations in two unknowns have the same solutions, then they are equivalent.  I can't seem to figure out how to prove this without resorting to case work where you account for the cases where one of the coefficients are zero and when both are.  Is there an elegant way to prove in general that when two systems of linear equations have the same solutions, they are equivalent? The converse is obvious enough though.  Definition of equivalence from the text :     Let us say that two systems of linear equations are equivalent if each equation in each system is a linear combination of the equations   in the other system. Suppose that I create Material001  and Material002  in Material Properties and set them to some color. Can I use this 2 items in other buttons like Texture Properties, Object Data Properties etc. ? Where and how do I intertwine them with this button ? How to ask "If you have any problem then ask me" in polite manner Error: j_id0:j_id1:j_id28:j_id30: Validation Error: Value is required So I've got the shout in my shouts list and I've unlocked all three parts of it, but I can't seem to be able to use it all, just the first part.  Am I missing something? I still have a quest for 'Learn the first word of Durnehviir's shout' but it's showing as me having already got it.  What gives? I need to extrude a circular shape from a surface that's basically just a grid of quads. What's the best practice to do this without screwing up the topology too much?  I basically want to have a circular face I can extrude, in order to have a cylinder like protuberance on the object, something like this: We use unit length Quaternion to represent rotations. Following is a general rotation matrix obtained ${\begin{bmatrix}m_{00} &amp; m_{01}&amp;m_{02} \\ m_{10} &amp; m_{11}&amp;m_{12}\\  m_{20} &amp; m_{21}&amp;m_{22}\end{bmatrix}}_{3\times 3}\tag 1 $.   How do I accurately calculate quaternion $q = q_1i+q_2j+q_3k+q_4$for this matrix?Means   how can we write $q_i$s interms of given $m_{ij}$  accurately? Is the Stack Overflow source code available? How to install TP-LINK T2UH Wireless adapter Driver (Ralink mt7610u) 14.04 --> 16.04 failed; apt (>= 1.0.1ubuntu2.13)' is not installed (This question was not resolved. Due to time constraints Computer was restored to factory settings.)  I was attempting to upgrade from 14.04 to 16.04, but apt threw this error:  The required dependency 'apt (&gt;= 1.0.1ubuntu2.13)' is not installed.   What does this mean, and how can I fix it?  When I type in the command apt-cache policy apt  Shageenth@shageenth-Inspiron-3451:~$ apt-cache policy apt apt: Installed: 1.0.1ubuntu2.11 Candidate: 1.0.1ubuntu2.11 Version table: *** 1.0.1ubuntu2.11 0 100 /var/lib/dpkg/status 1.0.1ubuntu2 0 500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64  Packages   The error happens when I run the command:   sudo do-release-upgrade -d   and it produces the following:  Checking for a new Ubuntu release Get:1 Upgrade tool signature [198 B] Get:2 Upgrade tool [1,265 kB] Fetched 1,265 kB in 0s (0 B/s) authenticate 'xenial.tar.gz' against 'xenial.tar.gz.gpg' extracting 'xenial.tar.gz'  Reading cache  Checking package manager Reading package lists... Done Building dependency tree Reading state information... Done Building data structures... Done  Required depends is not installed  The required dependency 'apt (&gt;= 1.0.1ubuntu2.13)' is not installed. How to list all installed packages I'd like to output a list of all installed packages into a text file so that I can review it and bulk-install on another system.  How would I do this? Isometries of the sphere $\mathbb{S}^{n}$ Got this as homework and I don't know how to tackle this. Help please!  Prove that the isometries of $\mathbb{S}^{n} \subset \mathbb{R}^{n+1}$, with the induced metric, are restrictions to $\mathbb{S}^{n}$ of the linear orthogonal transformations. Almost all standard sources on the existence of Majorana spinors (e.g. Appendix B.1 to Polchinski's "String Theory", Vol. 2) do so in a way I consider inherently ugly:   A priori, we are dealing with an irreducible complex representation $(V,\rho)$ of the Clifford algebra of signature $(p,q)$, i.e. generalized Dirac spinors. That Majorana spinors exist means abstractly that there is a  on $V$, i.e. a conjugate-linear map $\phi : V\to V$ with $\phi^2 = \mathrm{id}_V$ that commutes at least with the $\mathfrak{so}(p,q)$ action.  Every single source I can find for Majorana spinors uses operations like the transpose, complex conjugation and Hermitian adjoint on the $\Gamma$-matrices to obtain matrices acting on the same space. This is abstractly wrong, the transpose acts on the dual, the complex conjugation on the conjugate, and the Hermitian adjoint needs an inner product we have no reason for choosing. Of course, since $V$ is finite-dimensional, one can pick a basis and define the uncanonical isomorphisms to its dual and its conjugate, but I find this inelegant, particularly since the standard derivations require us to make a particular such choice with respect to the signs the $\Gamma$-matrices have under e.g. ${}^\dagger$. Finally, the Majorana spinors are usually defined by some equation involving an unnatural and arbitrary-looking product of $\Gamma$-matrices, which varies from source to source according to different sign conventions and sign choices made in the course of the derivation.  It's inelegant because the rest of the theory of spinors can be developed without making such uncanonical choices. Both the uniqueness of the dimension of the irreducible Dirac representations (there are two of them in odd dimensions) and the existence of the Weyl spinors in even dimensions can be derived purely from the abstract properties of the Clifford algebra, no choices made, no transpose, adjoint or conjugate occuring. The (admittedly slightly subjective question) is: Is there a way to show in which dimensions Majorana spinors exist that neither requires an uncanonical choice of basis nor arbitrary choices of signs?  Some partial results:   In even dimensions, the Dirac representation is necessarily self-conjugate since it is the only irreducible representation of the Clifford algebra, so all that is left to show is that a conjugate-linear $\mathfrak{so}$-equivariant map on it squares to $\mathrm{id}_V$ and not to $-\mathrm{id}_V$. However, I can't seem to exhibit any particular equivariant map on it that one could simply check for its square. In odd dimensions, one first needs to figure out whether the two inequivalent Dirac representations are conjugate to each other or self-conjugate.     As further motivation that a clear proof using only canonical properties of the Clifford algebra itself is required, consider the confusing and contradictory claims in the literature:   Polchinski, "String Theory", Vol. 2, p.434: $\mathrm{SO}(d-1,1)$ has Majoranas for $d = 0,1,2,3,4 \mod 8$, corresponding to a special case of $p-q = d-1-1 = 6,7,0,1,2 \mod 8$. Fecko, "Differential Geometry and Lie Groups for Physicists", pp. 651: $\mathrm{Cliff}(p,q)$ has Majoranas for $p-q = 0,2\mod 8$.  This clearly conflicts with Polchinski's claims e.g. for $d=3$. Figueroa-O'Farrill, , pp. 18: We have Majoranas for $p-q = 0,6,7\mod 8$ and "symplectic Majoranas" for $p-q = 2,3,4\mod 8$.   Note that these results conflict simply by the number of possible $p-q$ regardless of whether I've correctly taken care of the differing conventions of whether $p$ or $q$ denotes timelike dimensions. My foreign school book is not clearest at this point, what is really needed with this? What does it mean that "assign definite integral for $\lim_{n\rightarrow \infty}\sum_{k=1}^{n} \frac{1}{n+k}$"? I am not sure, whether I should assign it like this $\lim_{n\rightarrow \infty} \int_{1}^{n} \frac{1}{n+x} dx$ and noticing that it is continuous then trying to find borders so that $F(a) - F(b)$?  (the book messes up all kind of Leibniz stuff at this point, a bit messy -- and just stating $\int f(x)\,dx= F(a)-F(b)$, but not even paying attention to different borders. As far as I know, it is important to specify whether borders depend on the integration factor) Introduction to string theory In my textbook it is given that      'The wave function describes the position and state of the electron and its square gives the probability density of electrons.'    Can someone give me a very simple example of a wave function with explanation?  (Note: This question is not a duplicate. I have searched for other questions of this type but the answers were overwhelmingly difficult to understand.) Who wrote about an energy free space elevator? what is PGP public key block? There's PGP public key block posted on some websites (eg. ).  It's not hex code. it uses much more alphabet characters. What is it?  Why is this information posted? how can i use it? I am a grad student developing an interest for statistics. I like the material over-all, but I sometimes have a hard time thinking about applications to real life. Specifically, my question is about commonly used statistical distributions (normal - beta- gamma etc.). I guess for some cases I get the particular properties that make the distribution quite nice - memoryless property of exponential for example. But for many other cases, I don't have an intuition about both the importance and application areas of the common distributions that we see in textbooks.   There are probably a lot of good sources addressing my concerns, I would be glad if you could share those. I would be a lot more motivated into the material if I could associate it with real-life examples.