Diagonalization proof. ℝ is Uncountable – Diagonalization Let ℝ= all real numbers (expressibl...

A triangle has zero diagonals. Diagonals must be created across

5 Diagonalization of Operators 11 . 6 The Spectral Theorem 12 . 7 Simultaneous Diagonalization of Hermitian Operators 16 . 8 Complete Set of Commuting Observables 18 . 1 Uncertainty defined ... We are interested in the proof of the uncertainty inequality for it gives the information that is needed to find the conditions that lead to ...Diagonalization The proof we just worked through is called a proof by diagonalization and is a powerful proof technique. Suppose you want to show |A| ≠ |B|: Assume for contradiction that f: A → B is surjective. We'll find d ∈ B such that f(a) ≠ d for any a ∈ A. To do this, construct d out of “pieces,” one piece 8.2. Orthogonal Diagonalization 427 respectively. Moreover, by what appears to be remarkably good luck, these eigenvectors are orthogonal. We have kx1k2 =6, kx2k2 =5, and kx3k2 =30, so P= h √1 6 x1 √1 5 x2 √1 30 x3 i =√1 30 √ 5 2 √ 6 −1 −2 √ 5 √ √ 6 2 5 0 5 is an orthogonal matrix. Thus P−1 =PT and PTAP= 0 0 0 0 1 0 0 0 ... Proof. Homework Week 09. Lemma 3. Let A ∈ Rn×n with distinct eigenvalues. Let P = (v1 v2 ··· vn) be the matrix of eigenvectors and D = diag (λ1,λ2,...,λn) ...Diagonalization proof: A TM not decidable Sipser 4.11. Assume, towards a contradiction, that M ATM decides A. TM Define the TM D = "On input <M>: Run M. ATM. on <M, <M>>.If M. ATM accepts, reject; if M ATM. rejects, accept."Consider . running D on input <D>. Because D is a decider: either computation halts and accepts … or computation halts ...24 thg 2, 2017 ... What Are We Trying to Prove? Diagonalization is a mathematical proof demonstrating that there are certain numbers that cannot be enumerated.Theorem: A is diagonalizable if and only if A has an eigenbasis. Proof. Assume first that A has an eigenbasis {v1, · · · vn}. Let S be the matrix which contains these vectors as column vectors. Define B = S−1AS. Since Bek = S−1ASek = S−1Avk = S−1λkvk = λkS−1vk = λkek Nov 15, 2016 · Diagonalization proof: A TM not decidable Sipser 4.11 Assume, towards a contradiction, that it is. I.e. let M ATM be a Turing machine such that for every TM M and every string w, • Computation of M ATM on <M,w> halts and accepts if w is in L(M). • Computation of M ATM on <M,w> halts and rejects if w is not in L(M). If M 1 is TM with L(MExercise [Math Processing Error] 12.4. 1. List three different eigenvectors of [Math Processing Error] A = ( 2 1 2 3), the matrix of Example [Math Processing Error] 12.4. 1, associated with each of the two eigenvalues 1 and 4. Verify your results. Choose one of the three eigenvectors corresponding to 1 and one of the three eigenvectors ...Diagonalization The proof we just worked through is called a proof by diagonalization and is a powerful proof technique. Suppose you want to show |A| ≠ |B|: Assume for contradiction that f: A → B is surjective. We'll find d ∈ B such that f(a) ≠ d for any a ∈ A. To do this, construct d out of "pieces," one pieceDiagonalization Examples Explicit Diagonalization Theorem 5.2.3: With Distinct Eigenvalues Let A be a square matrix A, of order n. Suppose A has n distincteigenvalues. Then I the corresponding eigenvectors are linearly independent I and A is diagonalizable. Proof. I The second statement follows from the rst, by theorem 5.2.2. So, we prove the ... In set theory, Cantor's diagonal argument, also called the diagonalisation argument, the diagonal slash argument, the anti-diagonal argument, the diagonal method, and Cantor's diagonalization proof, was published in 1891 by Georg Cantor as a mathematical proof that there are infinite sets which cannot be put into one-to-one correspondence with t...• Cantor inspired by the diagonalization proof • Idea: • columns = 0,1 ∗ = inputs • rows = 0,1 ∗ ⊇Turing machines • 𝑀𝑀th row, 𝑥𝑥th column = (𝑀𝑀,𝑥𝑥) • If row not TM – fill with 0s. • If 𝑀𝑀does not halt on 𝑥𝑥enter 0. • Consider function that computes diagonal entries and flips them.Nov 21, 2016 · Question about Cantor's Diagonalization Proof. My discrete class acquainted me with me Cantor's proof that the real numbers between 0 and 1 are uncountable. I understand it in broad strokes - Cantor was able to show that in a list of all real numbers between 0 and 1, if you look at the list diagonally you find real numbers that are not …The Cantor diagonal method, also called the Cantor diagonal argument or Cantor's diagonal slash, is a clever technique used by Georg Cantor to show that the integers and reals cannot be put into a one-to-one correspondence (i.e., the uncountably infinite set of real numbers is "larger" than the countably infinite set of integers). However, Cantor's diagonal method is completely general and ...Moral: A proof \relativizes" if a) you (the prover) enumerate over Turing Machines, and b) use a Universal Turing Machine to simulate other Turing Machines. Observation Any diagonalization proof relativizes. Example Given a time function t;suppose we want to show DTIME O(t(n)) ( DTIME O(t(n)2) for any oracle O:We would simply go through the ... Thm. [B] Let X1,X2,··· ,Xk be eigenvectors corresponding to distinct eigenvalues λ1,λ2,··· ,λk of A. Then. {X1,X2,··· ,Xk} is linearly independent. Proof.The above resources directly prove the halting problem is not decidable via diagonalization - this proof is very similar to our poof for A TM.) Homework for next time: Watch the following video of my lecture on the topic, from 14:40 to the end (you can watch the beginning too, but that's material we have already covered). Proof: Assume for contradiction that the halting problem is decidable; (The halting problem is unsolvable) HALT TM is undecidable we will obtain a contradiction using the diagonalization technique An alternative proof: Basic idea: DIAGONALIZATION PROOF 22 H M w YESMhalts onw M doesn’t halt on NO w Suppose that is decidable HALT TM …Malaysia is a country with a rich and vibrant history. For those looking to invest in something special, the 1981 Proof Set is an excellent choice. This set contains coins from the era of Malaysia’s independence, making it a unique and valu...In this paper we prove the discrete convolution theorem by means of matrix theory. The proof makes use of the diagonalization of a circulant matrix to show that a circular convolution is diagonalized by the discrete Fourier transform. The diagonalization of the circular convolution shows that the eigenvalues of a circular convolution operator are …Proof. Homework Week 09. Lemma 3. Let A ∈ Rn×n with distinct eigenvalues. Let P = (v1 v2 ··· vn) be the matrix of eigenvectors and D = diag (λ1,λ2,...,λn) ...In set theory, Cantor's diagonal argument, also called the diagonalisation argument, the diagonal slash argument, the anti-diagonal argument, the diagonal method, and Cantor's diagonalization proof, was published in 1891 by Georg Cantor as a mathematical proof that there are infinite sets which cannot be put into one-to-one correspondence with the infinite set of natural numbers.Sep 17, 2022 · Theorem 7.2.2: Eigenvectors and Diagonalizable Matrices. An n × n matrix A is diagonalizable if and only if there is an invertible matrix P given by P = [X1 X2 ⋯ Xn] where the Xk are eigenvectors of A. Moreover if A is diagonalizable, the corresponding eigenvalues of A are the diagonal entries of the diagonal matrix D. Proof. Wiggle Aso that all eigenvalues of A(t) are di erent. There is now an orthonor-mal basis B(t) for A(t) leading to an orthogonal matrix S(t) such that S(t) 1A(t)S(t) = B(t) is diagonal for every small positive t. Now, the limit S(t) = lim t!0 S(t) and also the limit S 1(t) = ST(t) exists and is orthogonal. This gives a diagonalization S ...that p(A) = 0. This completes the proof of the Cayley-Hamilton theorem in this special case. Step 2: To prove the Cayley-Hamilton theorem in general, we use the fact that any matrix A ∈ Cn×n can be approximated by diagonalizable ma-trices. More precisely, given any matrix A ∈ Cn×n, we can find a sequence of matrices {A k: k ∈ N} such ...diagonalization; proof-theory; provability; Share. Cite. Follow edited Apr 4, 2021 at 21:16. Robin Saunders. asked Apr 2, 2021 at 16:14. Robin Saunders Robin Saunders. 884 6 6 silver badges 13 13 bronze badges $\endgroup$ 4 $\begingroup$ I don't understand your second paragraph. First of all, it seems to assume $\mathcal{T}$ is …In logic and mathematics, diagonalization may refer to: Matrix diagonalization, a construction of a diagonal matrix (with nonzero entries only on the main diagonal) that is similar to a given matrix. Diagonal argument (disambiguation), various closely related proof techniques, including: Cantor's diagonal argument, used to prove that the set of ...Sep 5, 2023 · Turing’s strategy was based on a mathematical technique called diagonalization that has a distinguished history. Here’s a simplified account of the logic behind his proof. String Theory Diagonalization stems from a clever trick for solving a mundane problem that involves strings of bits, each of which can be either 0 or 1. Lemma 1: Diagonalization is computable: there is a computable function diag such that n = dXe implies diag(n) = d(9x)(x=dXe^X)e, that is diag(n) is the Godel¤ number of the diagonalization of X whenever n is the Godel¤ number of the formula X. Proof sketch: Given a number n we can effectively determine whether it is a Godel¤ number Proof by contradiction Suppose that H is a program that solves the halting problem. Then, we can write the program D as follows: H solves the halting problem means the following: If D(x) halts then H(code(D),x) is true otherwise H(code(D),x) is false. Suppose that D(code(D)) halts. Then, by definition of H, it must be that H(code(D),code(D)) is ...diagonalization. The standard trick can be described as follows: make a (usually infinite) list of requirements (in the usual diagonalization proof the requirements are "the function I want to define has to be different from f_i , the i-th function on the list") for each i, find an input w(i) ("the i-th witness") such that w(i) shows thatDiagonalization proof: A TM not decidable Sipser 4.11 Assume, towards a contradiction, that M ATM decides A TM Define the TM D = "On input <M>: 1. Run M ATM on <M, <M>>. 2. If M ATM accepts, reject; if M ATM rejects, accept." Consider running D on input <D>. Because D is a decider: ! either computation halts and accepts …!Theorem 7.2.2: Eigenvectors and Diagonalizable Matrices. An n × n matrix A is diagonalizable if and only if there is an invertible matrix P given by P = [X1 X2 ⋯ Xn] where the Xk are eigenvectors of A. Moreover if A is diagonalizable, the corresponding eigenvalues of A are the diagonal entries of the diagonal matrix D.Diagonalization is the process of converting the matrix into the diagonal form. Visit BYJU’S to learn the theorem, proof and the diagonalization of 2×2 and 3×3 matrix with solved examples. Deer can be a beautiful addition to any garden, but they can also be a nuisance. If you’re looking to keep deer away from your garden, it’s important to choose the right plants. Here are some tips for creating a deer-proof garden.Jun 8, 2015 · The second example we’ll show of a proof by diagonalization is the Halting Theorem, proved originally by Alan Turing, which says that there are some problems that computers can’t solve, even if given unbounded space and time to perform their computations. Here the diagonalization means that the Hamiltonian is unitarily equivalent to the second quantization of a one-particle Hamiltonian, up to a constant. In many studies of quadratic Hamiltonians, Bogoliubov transformations were con- ... Proof. It is sufficient to show that F is bijective. For each f ∈ H , we put G(f) :=Cantor's diagonal proof is precisely proof of the fact that the rectangles never become squares. That's just a very straightforward ...Problem Five: Understanding Diagonalization. Proofs by diagonalization are tricky and rely on nuanced arguments. In this problem, we'll ask you to review the formal proof of Cantor’s theorem to help you better understand how it works. (Please read the Guide to Cantor's Theorem before attempting this problem.)We will use a proof technique called diagonalization to demonstrate that there are some languages that cannot be decided by a turing machine. This techniques ...This proof shows that there are infinite sets of many different “sizes” by considering the natural numbers and its successive power sets! The “size” of a set is called is cardinality. …Diagonalization is the process of finding the above and . Diagonalizing a matrix makes many subsequent computations easier. One can raise a diagonal matrix to a power by simply raising the diagonal entries to that power. The determinant of a diagonal matrix is simply the product of all diagonal entries.diagonalization; proof-theory; provability; Share. Cite. Follow edited Apr 4, 2021 at 21:16. Robin Saunders. asked Apr 2, 2021 at 16:14. Robin Saunders Robin Saunders. 884 6 6 silver badges 13 13 bronze badges $\endgroup$ 4 $\begingroup$ I don't understand your second paragraph. First of all, it seems to assume $\mathcal{T}$ is …Lecture 30: Diagonalization Diagonalization Two matrices are called similarif S−1AS. A matrix is called diagonalizableif it is similar to a diagonal matrix. A matrix is diagonalizable if and only if it has an eigenbasis, a basis consisting of eigenvectors. Proof. If we have an eigenbasis, we have a coordinate transformation matrix S which ... Cantor's Diagonal Argument: The maps are elements in N N = R. The diagonalization is done by changing an element in every diagonal entry. Halting Problem: The maps are partial recursive functions. The killer K program encodes the diagonalization. Diagonal Lemma / Fixed Point Lemma: The maps are formulas, with input being the codes of sentences. Dec 24, 2014 · 2 Answers. If you consider A, B A, B as quadratic forms, then, of course, they are simultaneously diagonalizable. That is, there is an invertible S S s.t. STBS = I,STAS = D S T B S = I, S T A S = D where D D is a diagonal matrix. Proof: diagonalize B B and B−1/2AB−1/2 B − 1 / 2 A B − 1 / 2. Since B−1/2AB−1/2 B − 1 / 2 A B − 1 / ...When a matrix is similar to a diagonal matrix, the matrix is said to be diagonalizable. We define a diagonal matrix D as a matrix containing a zero in every …172 Determinants and Diagonalization Solution. Let ak and jk denote, respectively,the number of adult and juvenilefemales after k years, so that the total female population is the sum ak +jk. Assumption 1 shows that jk+1 =2ak, while assumptions 2 and 3 show that ak+1 = 1 2ak + 1 4 jk. Hence the numbers ak and jk in successive yearsSo, the proof is: F = On input (A,B) where A and B are DFAs: Construct DFA C that is the symmetric difference of A and B (details on how to do this on next slide) Run TM T from the proof from last slide on input (C) If T accepts (sym. diff= ) then accept. If T rejects then reject * How to Construct C L (C) = (L (A) ∩ L (B)’) (L (A)’ ∩ L ...Proof: Suppose, for the sake of contradiction, that X were countable. Then there would exist a surjection f:N+X. We can construct a diabolical set Sp as follows: we include 3 in Sp, and for every; Question: (a) (5 pts) Identify and explain the flaw in the following diagonalization proof: Claim: Let X be the set of all subsets of N that contain ...The Cantor diagonal method, also called the Cantor diagonal argument or Cantor's diagonal slash, is a clever technique used by Georg Cantor to show that the integers and reals cannot be put into a one-to-one correspondence (i.e., the uncountably infinite set of real numbers is "larger" than the countably infinite set of integers). However, Cantor's diagonal method is completely general and ...This proof shows that there are infinite sets of many different “sizes” by considering the natural numbers and its successive power sets! The “size” of a set is called is cardinality. …The proof of this theorem will be presented explicitly for n = 2; the proof in the general case can be constructed based on the same method. Therefore, let A be 2 by 2, and denote its eigenvalues by λ 1 and λ 2 and the corresponding eigenvectors by v 1 and v 2 (so that A v 1 = λ 1 v 1 and A v 2 = λ 2 v 2 ).To summarize, we find a singular value decomposition of a matrix A in the following way: Construct the Gram matrix G = ATA and find an orthogonal diagonalization to obtain eigenvalues λi and an orthonormal basis of eigenvectors. The singular values of A are the squares roots of eigenvalues λi of G; that is, σi = √λi.Problem Two: Understanding Diagonalization Proofs by diagonalization are tricky and rely on nuanced arguments. In this problem, we'll ask you to re-view the formal proof of Cantor’s theorem to help you better understand how it works. (Please read the Guide to Cantor's Theorem before attempting this problem.) i.diagonalization proof or smaller steps can be determined in the Dichotomy paradox, new pages can always appear in the book where they are unexpected. All of these contradictions muddy our ability ...In set theory, Cantor's diagonal argument, also called the diagonalisation argument, the diagonal slash argument, the anti-diagonal argument, the diagonal method, and Cantor's diagonalization proof, was published in 1891 by Georg Cantor as a mathematical proof that there are infinite sets which cannot be put into one-to-one correspondence with t...The Cantor Diagonalization proof seems hard to grasp, and it ignites endless discussions regarding its validity. Also i have been reading similar threads here on stackexchange and im very sorry to keep beating this dead horse. Nevertheless i freely admit that i still do not understand the proof correctly. Also i'm not trying to disprove it. $\begingroup$ the Godel incompleteness theorem is seen somewhat to be a "different way"... another diagonalization proof relies on that the # of programs/input pairs is countable but languages are uncountable, and so in this way is similar to the incommensurability of the reals with the integers. see also this Q/A re Lawvere fixed point theorem ...Cantor’s diagonalization Does this proof look familiar?? Figure:Cantor and Russell I S = fi 2N ji 62f(i)gis like the one from Russell’s paradox. I If 9j 2N such that f(j) = S, then we have a contradiction. I If j 2S, then j 62f(j) = S. I If j 62S, then j 62f(j), which implies j 2S. 5Mar 29, 2021 · Eigenvectors and diagonalization • eigenvectors • dynamic interpretation: invariant sets • complex eigenvectors & invariant planes • left eigenvectors • diagonalization • modal form • discrete-time stability 11–1. Eigenvectors and eigenvalues λ ∈ C is an eigenvalue of A ∈ Cn×n ifThe Cantor diagonal method, also called the Cantor diagonal argument or Cantor's diagonal slash, is a clever technique used by Georg Cantor to show that the …29 thg 3, 2020 ... Step 2: there are only a countably infinite number of algebraic numbers. (N.B. We use Cantor's Diagonalisation argument in Step 3). Countably ...Diagonalization of Symmetric Matrices Let A 2Rn n be a symmtric matrix. Thm 1. Any two real eigenvectors pertaining to two distinct real eigenvalues of A are orthogonal. Proof: Let 1 and 2 be distinct eigenvalues of A, with Av 1 = 1 v 1; Av 2 = 2 v 2: so that 1 vT 2 v 1 = v T 2 (Av 1) = (Av 2) v 1 = 2 v T 2 v 1: This implies ( 2 1) vT 2 v 1 = 0 ...The above resources directly prove the halting problem is not decidable via diagonalization - this proof is very similar to our poof for A TM.) Homework for next time: Watch the following video of my lecture on the topic, from 14:40 to the end (you can watch the beginning too, but that's material we have already covered).8.2. Orthogonal Diagonalization 427 respectively. Moreover, by what appears to be remarkably good luck, these eigenvectors are orthogonal. We have kx1k2 =6, kx2k2 =5, and kx3k2 =30, so P= h √1 6 x1 √1 5 x2 √1 30 x3 i =√1 30 √ 5 2 √ 6 −1 −2 √ 5 √ √ 6 2 5 0 5 is an orthogonal matrix. Thus P−1 =PT and PTAP= 0 0 0 0 1 0 0 0 ... Diagonalization - Proof of Different Sized Infinities In order to prove that infinity has different sizes, Cantor formulated a test. We already know that in order for any size to be equal, there ...Mar 10, 2021 · Structure of a diagonalization proof Say you want to show that a set 𝑇𝑇is uncountable 1) Assume, for the sake of contradiction, that 𝑇𝑇is 2) “Flip the diagonal” to construct an element 𝑏𝑏∈𝑇𝑇such that 𝑓𝑓𝑛𝑛≠𝑏𝑏for every 𝑛𝑛 3) Conclude …A diagonalization proof is presented in section 4, and an explanation of the general usage of diagonalization follows. In section 5, universal languages are ...The proof will be by diagonalization, like what is used to prove the undecidability of the Halting Problem. Speci cally, we want to nd TM D such that: 1. D runs in time O(g(n)) 2. L(D) 6= L(M) for every TM M that runs in time f(n). First recall how (in cs121) an undecidable problem is obtained via diagonalization. x 1 x 2 x 3::: M 1 0 M 2 1::: 0In set theory, Cantor's diagonal argument, also called the diagonalisation argument, the diagonal slash argument, the anti-diagonal argument, the diagonal method, and Cantor's diagonalization proof, was published in 1891 by Georg Cantor as a mathematical proof that there are infinite sets which cannot be put into one-to-one correspondence with t... Mar 9, 2016 · (a)A proof that starts \Choose an arbitrary y2N, and let x= y2" is likely to be a proof that 8y2 N;8x2N;:::. Solution False. This would only be a proof that 9x2N with some property, not a proof that 8x2N the property holds. (b)The set of real numbers (R) is countable. Solution False. We proved this in class using diagonalization.Diagonalization of Symmetric Matrices Let A 2Rn n be a symmtric matrix. Thm 1. Any two real eigenvectors pertaining to two distinct real eigenvalues of A are orthogonal. Proof: Let 1 and 2 be distinct eigenvalues of A, with Av 1 = 1 v 1; Av 2 = 2 v 2: so that 1 vT 2 v 1 = v T 2 (Av 1) = (Av 2) v 1 = 2 v T 2 v 1: This implies ( 2 1) vT 2 v 1 = 0 ...Proof. First, we prove the “only if” part: if \(A\) is diagonalizable, it has \(n\) linearly independent eigenvectors. Observe that if \(P\) is any \(n\times n\) matrix with columns \(\mathbf{v}_1,\dots,\mathbf{v}_n,\) thenWe obtain from Theorem 1 and from its proof: Corollary. Let A,M be symmetric matrices of the same size, and let M be positive definite. Then all generalized eigenvalues (6) are real, and there is a basis of the whole space which consists of generalized eigenvectors. Proof. We refer to the proof of Theorem 1. Matrix (R−1)TAR−1 is sym- Diagonalization was also used to prove Gödel’s famous incomplete-ness theorem. The theorem is a statement about proof systems. We sketch a simple proof using Turing machines here. A proof system is given by a collection of axioms. For example, here are two axioms about the integers: 1.For any integers a,b,c, a > b and b > c implies that a > c. Sep 5, 2023 · Turing’s strategy was based on a mathematical technique called diagonalization that has a distinguished history. Here’s a simplified account of the logic behind his proof. String Theory Diagonalization stems from a clever trick for solving a mundane problem that involves strings of bits, each of which can be either 0 or 1. The proof of Theorem 9.22 is often referred to as Cantor’s diagonal argument. It is named after the mathematician Georg Cantor, who first published the proof in 1874. Explain the connection between the winning strategy for Player Two in Dodge Ball (see Preview Activity 1) and the proof of Theorem 9.22 using Cantor’s diagonal …Gödel's incompleteness theorems are two theorems of mathematical logic that are concerned with the limits of provability in formal axiomatic theories. These results, published by Kurt Gödel in 1931, are important both in mathematical logic and in the philosophy of mathematics.The theorems are widely, but not universally, interpreted as showing that …This proof shows that there are infinite sets of many different “sizes” by considering the natural numbers and its successive power sets! The “size” of a set is called is cardinality. How to Cite this Page: Su, Francis E., et al. “Cantor Diagonalization.” Math Fun Facts. <https://www.math.hmc.edu/funfacts>. References: . Proof: Suppose, for the sake of contradiction, that X were Proof. Assume first that A has an eigenbasis {v1, 8.2. Orthogonal Diagonalization 427 respectively. Moreover, by what appears to be remarkably good luck, these eigenvectors are orthogonal. We have kx1k2 =6, kx2k2 =5, and kx3k2 =30, so P= h √1 6 x1 √1 5 x2 √1 30 x3 i =√1 30 √ 5 2 √ 6 −1 −2 √ 5 √ √ 6 2 5 0 5 is an orthogonal matrix. Thus P−1 =PT and PTAP= 0 0 0 0 1 0 0 0 ... The most important application. The most important application of diagonalization is the computation of matrix powers. Let be a diagonal matrix: Then its -th power can be easily computed by raising its diagonal elements to the -th power: If a matrix is diagonalizable, then and Thus, all we have to do to raise to the -th power is to 1) diagonalize (if possible); 2) … In set theory, Cantor's diagonal argument, also called the diagon The proof of this theorem will be presented explicitly for n = 2; the proof in the general case can be constructed based on the same method. Therefore, let A be 2 by 2, and denote its eigenvalues by λ 1 and λ 2 and the corresponding eigenvectors by v 1 and v 2 (so that A v 1 = λ 1 v 1 and A v 2 = λ 2 v 2 ). I'll try to do the proof exactly: an infi...

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