Part number

A part number (often abbreviated PN, P/N, part no., or part #) is an identifier of a particular part design used in a particular industry. Its purpose is to simplify reference to that part. A part number unambiguously identifies a part design within a single corporation, and sometimes across several corporations.

For example, when specifying a screw, it is easier to refer to "HSC0424PP" than saying "Hardware, screw, machine, 4-40, 3/4" long, panhead, Phillips". In this example, "HSC0424PP" is the part number, and it may be prefixed in database fields as "PN HSC0424PP" or "P/N HSC0424PP".

The part design versus instantiations of it

As a part number is an identifier of a part design (independent of its instantiations), a serial number is a unique identifier of a particular instantiation of that part design. In other words, a part number identifies any particular (physical) part as being made to that one unique design; a serial number, when used, identifies a particular (physical) part (one physical instance), as differentiated from the next unit that was stamped, machined, or extruded right after it. This distinction is not always clear, as natural language blurs it by typically referring to both part designs, and particular instantiations of those designs, by the same word, "part(s)". Thus if you buy a muffler of P/N 12345 today, and another muffler of P/N 12345 next Tuesday, you have bought "two copies of the same part", or "two parts", depending on the sense implied.

Imaginary number

An imaginary number is a complex number that can be written as a real number multiplied by the imaginary unit i, which is defined by its property i² = −1. The square of an imaginary number bi is −b². For example, 5i is an imaginary number, and its square is −25. Except for 0 (which is both real and imaginary), imaginary numbers produce negative real numbers when squared.

An imaginary number bi can be added to a real number a to form a complex number of the form a + bi, where the real numbers a and b are called, respectively, the real part and the imaginary part of the complex number. Imaginary numbers can therefore be thought of as complex numbers whose real part is zero. The name "imaginary number" was coined in the 17th century as a derogatory term, as such numbers were regarded by some as fictitious or useless. The term "imaginary number" now means simply a complex number with a real part equal to 0, that is, a number of the form bi.

Some authors use the term pure imaginary number to denote what is called here an imaginary number, and imaginary number to denote any complex number that is not real (i.e. has non-zero imaginary part).

Number

A number is a mathematical object used to count, measure, and label. The original examples are the natural numbers 1, 2, 3, and so forth. A notational symbol that represents a number is called a numeral. In addition to their use in counting and measuring, numerals are often used for labels (as with telephone numbers), for ordering (as with serial numbers), and for codes (as with ISBNs). In common usage, the term number may refer to a symbol, a word, or a mathematical abstraction.

In mathematics, the notion of number has been extended over the centuries to include 0, negative numbers, rational numbers such as and , real numbers such as and , complex numbers, which extend the real numbers by including , and sometimes additional objects. Calculations with numbers are done with arithmetical operations, the most familiar being addition, subtraction, multiplication, division, and exponentiation. Their study or usage is called arithmetic. The same term may also refer to number theory, the study of the properties of the natural numbers.

Voter ID laws

A voter ID law is a law that requires a person to have some form of identification to vote or receive a ballot for an election. In most jurisdictions, voters must present an ID, usually a photo ID. Because of perceptions of a differing ability to obtain identification on the basis of socioeconomic status, age, or race, some people in the United States and Canada consider them controversial.

Brazil

In Brazil voting is compulsory to all citizens between 18 and 70 years old. To vote, all citizens must:

Since 2006 the Brazilian Electoral Justice is re-registering voters with biometric identification. In the 2014 elections more than 22 million voters out of 141 million will be identified by fingerprints.

Canada

Federal elections

In Canada, the Federal government mails an Elections Canada registration confirmation card, which the voter takes to the polling station. The card tells the individual where and when to vote. Voters must prove their identity and address with one of three options:

Identity document

An identity document (also called a piece of identification or ID, or colloquially as papers) is any document which may be used to identify a person or verify aspects of a person's personal identity. If issued in a small, standard credit card size form, it is usually called an identity card (IC or ID card). Some countries issue formal identity documents, while others may require identity verification using informal documents. When the identity document incorporates a person's photograph, it may be called photo ID.

In the absence of a formal identity document, a driver's license may be accepted in many countries for identity verification. Some countries do not accept driver's licenses for identification, often because in those countries they do not expire as documents and can be old or easily forged. Most countries accept passports as a form of identification.

Some countries require foreigners to have a passport or occasionally a national identity card from their country available at any time if they do not have a residence permit in the country.