In mathematics, −1 is the additive inverse of 1, that is, the number that when added to 1 gives the additive identity element, 0. It is the negative integer greater than negative two (−2) and less than 0.

Negative one has some similar but slightly different properties to positive one.

Negative one bears relation to Euler's identity since Failed to parse (Missing texvc executable; please see math/README to configure.): e^{i \pi} = -1.\!

In computer science, −1 is a common initial value for integers and is also used to show that a variable contains no useful information.

Multiplying a number by −1 is equivalent to changing the sign on the number. This can be proved using the distributive law and the axiom that 1 is the multiplicative identity: for x real, we have

where we used the fact that any real x times 0 equals 0, implied by cancellation from the equation

In other words,

so (−1) · x is the arithmetic inverse of x, or −x.

The square of −1, i.e. −1 multiplied by −1, equals 1. As a consequence, a product of negative real numbers is positive.

A number is a mathematical object used to count and measure. In mathematics, the definition of number has been extended over the years to include such numbers as zero, negative numbers, rational numbers, irrational numbers, and complex numbers.

Mathematical operations are certain procedures that take one or more numbers as input and produce a number as output. Unary operations take a single input number and produce a single output number. For example, the successor operation adds one to an integer, thus the successor of 4 is 5. Binary operations take two input numbers and produce a single output number. Examples of binary operations include addition, subtraction, multiplication, division, and exponentiation. The study of numerical operations is called arithmetic.

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 (telephone numbers), for ordering (serial numbers), and for codes (e.g., ISBNs).

DJ Wich (also known as Tomáš Pechlák) is a DJ who works the Czech/Slovkia hip-hop scene. He started DJing in 1998.

In 1993, DJ Wich met Indy and LA4 on a graffiti scene. In 1998 they formed Indy & Wich, where Indy performed as a rapper and DJ Wich as producer. They often work with rapper LA4 in live performances.

In 2002, they released their debut album My3. Their second album Hádej kdo… was nominated on Anděl in 2006. The following year they produced The Chronicles of Nomad with rapper Nironic.

In 2008, DJ Wich released his first solo album The Golden Touch with international stars like Lil Wayne, Talib Kweli, M.O.P, Kurupt and more.

He collaborated with Czech artists, including Orion, Hugo Toxxx, W518, LA4 and from the international Rasco, Rytmus, H16, Vec, and Nironic.

Wich streams live shows from (DJ Wich Live TV) with other rappers, live recording, interviews and chat.

DJ Wich made soundtracks for Czech movie Gympl and Ulovit miliardáře which was released on 1 October 2008 with Tomáš Vorel as director.