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  2. Sylvester–Gallai theorem - Wikipedia

    en.wikipedia.org/wiki/Sylvester–Gallai_theorem

    A line that contains exactly two of a set of points is known as an ordinary line. Another way of stating the theorem is that every finite set of points that is not collinear has an ordinary line. According to a strengthening of the theorem, every finite point set (not all on one line) has at least a linear number of ordinary lines.

  3. Cantor's diagonal argument - Wikipedia

    en.wikipedia.org/wiki/Cantor's_diagonal_argument

    Cantor's diagonal argument (among various similar names [note 1]) is a mathematical proof that there are infinite sets which cannot be put into one-to-one correspondence with the infinite set of natural numbers – informally, that there are sets which in some sense contain more elements than there are positive integers.

  4. Mathematical proof - Wikipedia

    en.wikipedia.org/wiki/Mathematical_proof

    Then P(n) is true for all natural numbers n. For example, we can prove by induction that all positive integers of the form 2n − 1 are odd. Let P(n) represent " 2n − 1 is odd": (i) For n = 1, 2n − 1 = 2 (1) − 1 = 1, and 1 is odd, since it leaves a remainder of 1 when divided by 2. Thus P(1) is true.

  5. Cantor set - Wikipedia

    en.wikipedia.org/wiki/Cantor_set

    Cantor set. In mathematics, the Cantor set is a set of points lying on a single line segment that has a number of unintuitive properties. It was discovered in 1874 by Henry John Stephen Smith [1][2][3][4] and mentioned by German mathematician Georg Cantor in 1883. [5][6] Through consideration of this set, Cantor and others helped lay the ...

  6. Collatz conjecture - Wikipedia

    en.wikipedia.org/wiki/Collatz_conjecture

    As an illustration of this, the parity cycle (1 1 0 0 1 1 0 0) and its sub-cycle (1 1 0 0) are associated to the same fraction ⁠ 5 / 7 ⁠ when reduced to lowest terms. In this context, assuming the validity of the Collatz conjecture implies that (1 0) and (0 1) are the only parity cycles generated by positive whole numbers (1 and 2 ...

  7. Euclid's theorem - Wikipedia

    en.wikipedia.org/wiki/Euclid's_theorem

    Paul Erdős gave a proof [11] that also relies on the fundamental theorem of arithmetic. Every positive integer has a unique factorization into a square-free number r and a square number s 2. For example, 75,600 = 2 4 3 3 5 2 7 1 = 21 ⋅ 60 2. Let N be a positive integer, and let k be the number of primes less than or equal to N. Call those ...

  8. Deduction theorem - Wikipedia

    en.wikipedia.org/wiki/Deduction_theorem

    Deduction theorem. In mathematical logic, a deduction theorem is a metatheorem that justifies doing conditional proofs from a hypothesis in systems that do not explicitly axiomatize that hypothesis, i.e. to prove an implication A → B, it is sufficient to assume A as a hypothesis and then proceed to derive B. Deduction theorems exist for both ...

  9. Cantor's intersection theorem - Wikipedia

    en.wikipedia.org/wiki/Cantor's_intersection_theorem

    A simple corollary of the theorem is that the Cantor set is nonempty, since it is defined as the intersection of a decreasing nested sequence of sets, each of which is defined as the union of a finite number of closed intervals; hence each of these sets is non-empty, closed, and bounded. In fact, the Cantor set contains uncountably many points.