Question: The rapper of For Whom the Beat Tolls is one half of what group? 

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Gimlet (cocktail): The gimlet (pronounced with a hard 'g') is a cocktail made of gin and lime juice.  A 1928 description of the drink was: "gin, a spot of lime, and soda".  The description in the 1953 Raymond Chandler novel "The Long Goodbye" stated that "a real gimlet is half gin and half Rose's lime juice and nothing else".  This is in line with the proportions suggested by "The Savoy Cocktail Book" (1930) which specifies one half Plymouth Gin and one half Rose's Lime Juice Cordial.  However, modern tastes are less sweet, and generally provide for at least two parts gin to one part of the lime and other non alcoholic elements (see recipes below).

Fat Jon: Jon Marshall (born September 6, 1975), better known by his stage name Fat Jon the Ample Soul Physician, is an American hip hop producer and rapper from Cincinnati, Ohio.  He is a member of the American hip-hop group Five Deez.  He is also one half of 3582 with J. Rawls, one half of Rebel Clique with vocalist Amleset Solomon, and one half of Beautiful Killing Machine with Sonic Brown of Five Deez.  Fat Jon is also credited as part of the production team that scored the music for the anime series "Samurai Champloo".  He currently resides in Frankfurt, Germany.

Royce da 5'9&quot;: Ryan Daniel Montgomery (born July 5, 1977), better known by his stage name Royce da 5′9″, is an American rapper from Detroit, Michigan.  He is best known for his longtime association with Eminem as well as his solo career, recording primarily with producers Carlos "6 July" Broady and DJ Premier, as well as ghostwriting for the likes of Diddy and Dr. Dre.  Royce is one half of the rap duo Bad Meets Evil with Eminem, one quarter of the hip hop group Slaughterhouse with Joe Budden, Joell Ortiz and Crooked I, and one half of the hip hop group PRhyme with DJ Premier.  The editors of About.com ranked him No. 30 on their list of the Top 50 MCs of Our Time (1987–2007).

For Whom the Beat Tolls: For Whom the Beat Tolls (a play on the Ernest Hemingway novel 'For Whom the Bell Tolls', which itself is drawn from "Meditation XVII" of "Devotions upon Emergent Occasions", a series of essays by metaphysical poet John Donne) is the eighth studio album by rapper Canibus, released through Mic Club Music on May 29, 2007 in the United States and June 5 worldwide.  It features the new "Poet Laureate Infinity" concept, which involves mixing 200 bar layers with corresponding ones in order to create various subject matter, rhymes and overall sound.  The album leaked on the Internet on June 4, 2007.  According to Canibus' DJ, Puerto Roc, the album has sold 60,000 copies as of October 2007.

Orikal Uno: Antonio Rosario (born July 27, 1989), better known as Orikal Uno, is an American rapper from Saint Paul, Minnesota.  Orikal Uno is one half of the hip-hop group OnePlusOne, which was founded with Alphonso Fleming Jr (DisputeOne).  He is one half of the hip-hop group spellbound along with DJ Greenery.  Orikal Uno is known as a visual artist; painting custom canvases for people via multiple platforms on the internet.  He is also a notable music producer and audio engineer.

Machinedrum: Travis Stewart (born March 4, 1982), better known as Machinedrum, is an American electronic music producer and performer from North Carolina.  He is also known as Syndrone and Tstewart.  He is one half of Sepalcure, with Praveen Sharma, one half of Jets, with Jimmy Edgar, as well as half of Dream Continuum, with Jim Coles, a.k.a. Om Unit.

Mr. J. Medeiros: Jason C. Medeiros better known as Mr. J. Medeiros, is an American Rapper, Record Producer, and Songwriter.  As well as releasing music under the name, Mr. J. Medeiros, he is responsible for forming the Hip Hop group The Procussions, is one half of the Hip Hop/Electronic duo AllttA, and the lead singer of Punk-Rap group KNIVES.  He is of Portuguese and Scottish descent.  Mr. J. has written music with such artists as, Monte Nueble, Noel Zancanella, Randy Jackson, Marty James, Shad (rapper), George "Spanky" McCurdy, Symbolyc One (S1), Illmind, Benny Cassette, Talib Kweli, 20Syl and French hip hop group Hocus Pocus (group) and more famous C2C.

Unihemispheric slow-wave sleep: Unihemispheric slow-wave sleep (USWS) is sleep with one half of the brain while the other half remains alert.  This is in contrast to normal sleep where both eyes are shut and both halves of the brain show reduced consciousness.  In USWS, also known as asymmetric slow-wave sleep, one half of the brain is in deep sleep, a form of non-rapid eye movement sleep and the eye corresponding to this half is closed while the other eye remains open.  When examined by low voltage electroencephalography (EEG), the characteristic slow-wave sleep tracings are seen from one side while the other side shows a characteristic tracing of wakefulness.  The phenomenon has been observed in a number of terrestrial, aquatic and avian species.

Canibus: Germaine Williams (born December 9, 1974), better known by his stage name Canibus, is an American rapper and actor.  He is a member of The HRSMN, Sharpshooterz, Cloak N Dagga, The Undergods, and one-half of T.H.E.M. Canibus rose to fame in the mid-nineties.  About.com placed him at number 32 on their list of the "Top 50 MCs of Our Time (1987–2007)", while in 2012 "The Source" placed him number 44 on their list of the Top 50 Lyricists of All Time.

One half: One half is the irreducible fraction resulting from dividing one by two (⁄ ), or the fraction resulting from dividing any number by its double.  Multiplication by one half is equivalent to division by two, or "halving"; conversely, division by one half is equivalent to multiplication by two, or "doubling".  One half appears often in mathematical equations, recipes, measurements, etc.  Half can also be said to be one part of something divided into two equal parts.

Supporting paragraphs: For Whom the Beat Tolls Canibus
Answer: T.H.E.M.