Please help me to figure this out. Born into a dysfunctional family, Marty1 alters his parents 1955 timeline. In this new, functional family timeline, Marty2 is born and raised until he disappears in his timeline's Delorean. Dysfunctional family timeline's Marty1 accomplished his mission and returned to Marty2's timeline, which left Marty2 nothing to alter in 1955(since Marty1 was already in 1955 doing the things shown the film), and as far as I can tell, Marty2 isn't represented in the rest of the trilogy. Did the film series leave a gaping plot hole, or am I just confused??
In  (the original movie), Marty comes back from 1955 10 mins early to prevent Doc from being shot (which he fails at). He then rolls up to the Lone Pine Mall and sees himself hit 88 mph and shoot back to 1955 (again). Marty then carries on with this life as usual. What happens to the Marty that goes back to 1955 at the end of the film?  This obviously is a recursive problem where it would create another timeline and Marty would keep coming back 10 mins early to view another Marty zip back to 1955?
Why is "cupboard" pronounced with a silent "p"? Why does this formulation of Choice not follow from the Comprehension Schema? Why is there this strange contradiction between the language of logic and that of set theory? In standard probability theory events are represented by sets consisting of elementary events. Consider two events for which (as sets) $A \subset B$. If an elementary event $x \in A$ takes places then we say that $B$ takes place as well. Since $A \subset B$, $x \in A$ implies that $B$ takes place too.  It seems that when for sets (representing events) $$A \subset B$$ $$then \ A \ implies \ B .$$  On the other hand, if we use the language of logic for the events then $$A \supset B$$ $$ \ means\  that \ A\  implies\ B .$$  Why is this strange virtual contradiction between the language of sets and the language of logic?  (In order to avoid down votes and unplesant comments I reveal that I happen to know that the true translation of the sentence $A \supset B$ of logic to the language of sets (representing events) is $\overline{A \cap \overline B}$.) It is possible to find an efficient algorithm for constructing a provably hard to factor number $N$, together with a witness that shows that it is indeed hard to factor. EDIT, since it was not clear: I also want to be sure that even the person that constructed the number cannot factor it.  Of course, a random large enough integer is going to be hard to factor with high probability, but we might be unlucky.  There are also multi-party protocols for shared generation of RSA moduli (such as ), but I would like a non interactive technique.  Motivation: This was suggested by Poncho's answer to Converting from DMS to DD using Python in Field Calculator? Number of zero digits in factorials Here is a riddle someone has been asked in a job interview: How many zero digits are there in $100!$?  Well, I found the first $24$ quite fast by counting how many times five divides $100!$ ($5$ divides $20$ times and $25$ divides it $4$ times).   However, there are more zero digits in the middle of the number (these can be found by hand, by typing factorial(100) in sage).  My question is whether there is a smart way to determine the number of zero digits in $100!$, and more generally in $n!$.  By the way, this will not affect the job interview as it was finished some time ago. How could I retrive full internal storage of an Android smartphone in order to restore data? After reading of:  I wonder if the  also applies to flagging of old questions.  I have the subjective feeling the longer the time between the question and the flagging is, the longer it takes to become reviewed.   Is flagging of old posts a waste of moderator time? Should I avoid that? Some questions about Hilbert matrix This Exercise $12$ page $27$ from Hoffman and Kunze's book Linear Algebra.     The result o Example $16$ suggests that perhaps the matrix      $$A = \begin{bmatrix} 1 &amp; \frac{1}{2} &amp; \ldots &amp; \frac{1}{n}\\  \frac{1}{2} &amp; \frac{1}{3} &amp; \ldots &amp; \frac{1}{n+1}\\ \vdots &amp; \vdots &amp;  &amp; \vdots \\ \frac{1}{n} &amp;\frac{1}{n+1} &amp;\ldots &amp;\frac{1}{2n-1} \end{bmatrix}$$      is invertible and $A^{-1}$ has integer entries. Can you prove that?   I will copy their words before that example:      Some people find it less awkward to carry along two sequences of   matrices, one describing the reduction of $A$ to the identity and the   other recording the effect of the same sequence of operations starting   from the identity.   In this , Adrián Barquero says:      If your linear algebra textbook is Kenneth Hoffmann and Ray Kunze's   Linear Algebra book then I was in the same situation you're right now   a few years ago, but I was adviced at the moment that this particular   exercise wasn't as easy as one might expect at first.      The matrix you have is called the Hilbert matrix and the question you   have was already asked a couple of times in math overflow  and   . They have excellent answers so I will just point you to them.   My question: Is it possible answer the question made by the authors without using high techniques?  I am not allowed to use determinants here.  PS: Those answers in MO don't answer the question above. I apologise if this question is unappropriated or if I was unable to understand their answers. Is it possible to shutdown remote Computers without inputing the password? I used the following bash to shutdown remote computers,but for each computer,I must input the password for it.Is it possible to input the password Automatically?   #!/bin/bash  ssh -t root@192.168.1.11 "sudo poweroff" ssh -t root@192.168.1.12 "sudo poweroff" ssh -t root@192.168.1.13 "sudo poweroff" ssh -t root@192.168.1.14 "sudo poweroff" ssh -t root@192.168.1.15 "sudo poweroff" ssh -t root@192.168.1.16 "sudo poweroff" ssh -t root@192.168.1.17 "sudo poweroff" ssh -t root@192.168.1.18 "sudo poweroff" ssh -t root@192.168.1.19 "sudo poweroff" ssh -t root@192.168.1.20 "sudo poweroff" ssh -t root@192.168.1.21 "sudo poweroff" ssh -t root@192.168.1.22 "sudo poweroff" ssh -t root@192.168.1.23 "sudo poweroff" ssh -t root@192.168.1.24 "sudo poweroff" ssh -t root@192.168.1.25 "sudo poweroff" ssh -t root@192.168.1.26 "sudo poweroff" Story about building up speed leading to increased quality of life So I was reading this:  and while the answers for the first question are good, nobody gave much attention to the second one. In fact, people only said that it can be proved without giving any proof or any.  So, if I have a Lagrangian and ADD an arbitrary function of $\dot{q}$, $q$ and $t$ in such a way that the equations of motion are the same, does this extra function MUST be a total time derivative?   EDIT Ok, I changed my question a little bit:  Question: If I have a function that obeys the Euler-Lagrange equation off-shell, this implies that my function is a time derivative? (This was used in Qmechanic's answer of this other question: , equation 14.)  Also, why people only talk about things that change the Lagrangian only by a total derivative? If this is not always the case that keeps the equation of motion the same, so why is it so important? And why in the two questions I posted about the same statement on Landau&amp;Lifshitz's mechanics book only consider this kind of change in the Lagrangian? Add tab / local task to a node I've created a module called hotel_reviews.  I've created the route node/{node}/reviews using .   hotel_reviews.content:   path: '/node/{node}/reviews'   defaults:     _controller: '\Drupal\hotel_reviews\Controller\ReviewsController::content'     _title: 'Reviews'   requirements:     _permission: 'access content'   I then tried to add a local task using .  hotel_reviews.content:   route_name: hotel_reviews.content   title: 'Reviews'   base_route: node.view   weight: 100   I can now access the content defined by my controller at node/1/reviews, however when I go to node/1 I don't see a reviews tab.  What am I doing wrong?  I've been using the following documentation so far: Can an infectious diseases come from a plant? Coronavirus, HIV, 1918 Flu, etc. They all come from animals. Do any infectious diseases (in humans) come from plants? More specifically, are there viruses that infect plants that can mutate to infect humans? I know that any group satisfying $x^2=1$ for all $x$ is abelian. Is the same true if $x^3=1$? I don't think it is, but I can't find a basic counterexample. When and how did "pretty" enter English as an intensifying adverb? I recently updated my profile bio (from Arqade) and clicked 'Save and copy changes to all public communities'. This appears to have broken/reset my profile picture on all but Arqade. Note that I did not update my profile picture as part of my changes. Arqade:  Meta SE for comparison:  I haven't touched my profile picture in years. Is this a bug?  Update: It appears my profile pic across all communities has been set back to 'Identicon'. I went on to Stack Overflow and changed my profile picture back to 'Gravitar' and clicked 'Save and copy to all communities' again, but this did not update my profile picture anywhere but SO. (I did the same on Sustainability to be doubly sure). Update 2: This is a persistent bug - I had changed most of my SE communities back to my 'Robotnik' display pic over the past little while. Today I edited my profile again on Arqade, Clicked 'Save and copy' - and the display pic reverted back to identicon again across all sites. Update 3: I have re-uploaded my profile picture and the 'Save and copy' function worked. It appears that this is actually a bug to do with the old images from Gravatar. Case-insensitive attribute-value selector with Jquery Biometric information for a UK visitor visa for the second time I submitted my biometric information when I applied for (and successfully received) the UK visitor visa.  Now, the visa has expired and I would like to apply for it again.   Do I need to submit my biometric information again?  Will the process be the exact same as before? Are Living Beings Turned Into Horcruxes Suceptible to Age, Disease, or Injury? From the HP books I know that Horcruxes grant a form of immortality. So, it is not possible for someone who created a Horcrux to die from old age or succumb to diseases. I guess the same is true for living beings turned into a Horcrux. But do living Horcruxes age normally? Is it possible to cripple them or sever their limbs, head or something like that, or do they instantly "repair" themselves like inanimate Horcruxes?