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  2. Constructive proof - Wikipedia

    en.wikipedia.org/wiki/Constructive_proof

    Constructive proof. In mathematics, a constructive proof is a method of proof that demonstrates the existence of a mathematical object by creating or providing a method for creating the object. This is in contrast to a non-constructive proof (also known as an existence proof or pure existence theorem), which proves the existence of a particular ...

  3. United States Proof Set - Wikipedia

    en.wikipedia.org/wiki/United_States_Proof_Set

    United States Proof Set. The United States Mint Proof Set, commonly known as the Proof Set in the United States, is a set of proof coins sold by the United States Mint. The proof set is popular with coin collectors as it is an affordable way to collect examples of United States coinage in proof condition.

  4. Sheldon coin grading scale - Wikipedia

    en.wikipedia.org/wiki/Sheldon_coin_grading_scale

    Proof coins. Like circulated grades, proof coins are graded on the Sheldon scale from 1 to 70, and are preceded by the abbreviation ‘PF’ or ‘PR’ to distinguish them from circulation strikes. Proof coins graded 60 to 70 are mirrored to those of Uncirculated grades with the difference that the coin was not made for circulation.

  5. Proof coinage - Wikipedia

    en.wikipedia.org/wiki/Proof_coinage

    Proof coinage refers to special early samples of a coin issue, historically made for checking the dies (as in demonstrating that something is true) and for archival purposes. In modern times, proofs are often struck in greater numbers, especially for coin collectors (numismatists). [1] Nearly all countries have issued proof coinage.

  6. 6 Coins From the 1970s That Are Worth a Lot of Money - AOL

    www.aol.com/6-coins-1970s-worth-lot-154319500.html

    1979 Susan B. Anthony Dollar Over 1978 Jefferson Nickel: $15,275. This coin features a minting mistake with the image of Susan B. Anthony stamped over the top of Monticello on a Jefferson nickel ...

  7. United States Mint coin sets - Wikipedia

    en.wikipedia.org/wiki/United_States_Mint_coin_sets

    United States currency was debased beginning in 1965, but the sets continued under the name United States Mint Proof Set. Production was moved to the San Francisco branch in 1968, and all subsequent issues bear coins with an "S" mint mark. In 1973, the Eisenhower dollar was added to the collection. Sets from 1975 will have a dual-date 1776-1976 ...

  8. 5 Coins From the 1960s That Are Worth a Lot of Money - AOL

    www.aol.com/5-coins-1960s-worth-lot-190430304.html

    1960 Ben Franklin Half Dollar. Like quarters from the early 60s, half dollars were produced using real silver. That means a 1960 Ben Franklin half dollar is worth at least $11 or $12 today, with ...

  9. Intuitionistic logic - Wikipedia

    en.wikipedia.org/wiki/Intuitionistic_logic

    Intuitionistic logic, sometimes more generally called constructive logic, refers to systems of symbolic logic that differ from the systems used for classical logic by more closely mirroring the notion of constructive proof. In particular, systems of intuitionistic logic do not assume the law of the excluded middle and double negation ...

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