Question: Jeffrey Walker and Fat Mike, share which mutual occupation?

full_context: Document 1: Fat Wreck Chords: Fat Wreck Chords (pronounced as if spelled "Fat Records", ) is a San Francisco, California-based independent record label, focused on punk rock. It was started by NOFX lead singer Michael Burkett (better known as Fat Mike) and his girlfriend at the time, Erin Burkett, in 1991.
Document 2: Zakk Wylde: Zakk Wylde (born Jeffrey Phillip Wielandt on January 14, 1967) is an American musician, singer, songwriter, multi-instrumentalist and occasional actor who is best known as the guitarist for Ozzy Osbourne, and founder of the heavy metal band Black Label Society. His signature bulls-eye design appears on many of his guitars and is widely recognized. He was the lead guitarist and vocalist in Pride & Glory, who released one self-titled album in 1994 before disbanding. As a solo artist he released "Book of Shadows" and "Book of Shadows II".
Document 3: Jeff Pezzati: Jeffrey Neal "Jeff" Pezzati is the lead singer for the popular Chicago punk band, Naked Raygun. From 1983 to 1985, he was also the bass player for the internationally known band Big Black. In 1980, Jeff Pezzati was a member of a suburban cover band, Condor, when he was asked to audition for Naked Raygun (then known as Negro Commando) by the founders, Santiago Durango and Jeff's brother, Marco Pezzati. Jeff passed the audition and became the band's longest-running member.
Document 4: Mike Dean (musician): Mike Dean (born Thomas Michael Dean on August 24, 1963) is the bassist for American metal band Corrosion of Conformity. He sang on the band's early recordings from their crossover thrash era before leaving the band in 1987. In 1989 Dean, along with C.O.C. guitarist Woody Weatherman and artist Brian Walsby on drums, released the Snake Nation album on Caroline Records. Dean rejoined C.O.C. as the bass player and occasional vocalist in 1993 and has remained with the band since. Along with several production and engineering credits he also collaborated with Dave Grohl on the Probot song "Access Babylon", a return to the punk/metal fusion of old.
Document 5: Jeffrey Walker: Jeffrey Walker (born 25 March 1969) is a bass guitarist, vocalist from Windle, St Helens, UK. He is best known for his work with death metal band Carcass for which he is also the main lyricist. Before Carcass, he played in the hardcore punk band Electro Hippies. After the demise of Carcass, he went on to form hard rock band Blackstar with two former Carcass bandmates. In some territories the band was called Blackstar Rising.
Document 6: Mike Viola: Michael "Mike" Viola is a Grammy-nominated producer, musician, songwriter and singer best known for his work with Ryan Adams, Jenny Lewis, Andrew McMahon, New Politics, and Fall Out Boy. His original music has been featured on soundtracks for movies such as "Get Him to the Greek", "" and "That Thing You Do!".
Document 7: Bill Steer: Bill Steer (born William Geoffrey Steer, 3 December 1969) is a British guitar player, and co-founder of the extreme metal band Carcass. He is considered a pioneer and an essential contributor to grindcore and death metal due to his involvement in Napalm Death and Carcass, two of the most important bands of those genres. Presently he plays with Gentlemans Pistols, the reactivated Carcass and appears as a live second guitarist for Angel Witch.
Document 8: Kirk Windstein: Kirk Windstein (born April 14, 1965) is an American musician. He is a founding member of the sludge metal band Crowbar, and formerly played with the heavy metal band Down from 1991 to 2013. In 2005, Windstein formed Kingdom of Sorrow with Jamey Jasta of Hatebreed. Their debut album was released in 2008. Windstein began his musical career in 1985 as a guitarist for a cover band called Victorian Blitz, and in 1988 joined a hardcore punk band called Shell Shock as a vocalist and guitarist.
Document 9: Fat Mike: Michael John Burkett (born January 31, 1967), also known as Fat Mike, is an American musician and producer. He is the bassist and lead vocalist for the punk rock band NOFX and the bassist for the punk rock supergroup cover band Me First and the Gimme Gimmes. He was also a temporary bassist for the band Against Me!
Document 10: Mike Tempesta: Mike Tempesta is a rock guitarist and an artist relations manager. He also goes by the moniker "M.33". He was credited for rhythm guitar on the 1990 Anthrax album "Persistence of Time". Before his career as a musician, he was a guitar technician for Anthrax's Scott Ian. He was a member of Human Waste Project, and played rhythm guitar in the band Powerman 5000 until his departure in 2005. He performed on the debut album of Scum of the Earth, once again with his brother John Tempesta, and has since left the lineup. After leaving Powerman 5000, he took up a job as an artist relations manager for Yamaha Corporation of America, but soon left and eventually was hired as an artist relations manager for Fender Musical Instruments Corporation, overseeing the Jackson, Charvel, and EVH brands.
Document 11: Mike Patton: Michael Allan "Mike" Patton (born January 27, 1968) is an American musician, singer, songwriter, actor, record producer, multi-instrumentalist and film composer, best known as the lead singer of the alternative metal band Faith No More. Patton was also the founder and lead singer of Mr. Bungle, and has played with Tomahawk, Fantômas, Lovage, The Dillinger Escape Plan, and Peeping Tom.
Document 12: Mike Muir: Michael Allen "Mike" Muir (born March 14, 1963) is the lead vocalist of the Venice, California crossover thrash bands Suicidal Tendencies, Los Cycos and the funk metal band Infectious Grooves. He has also released several solo albums under his nickname Cyco Miko. Muir's trademark is wearing bandanas, jerseys with the number 13, and hats with block style letters that read "Suicidal".
Document 13: Jeff Hanneman: Jeffrey John "Jeff" Hanneman (January 31, 1964 – May 2, 2013) was an American musician, best known as a founding member of the American thrash metal band Slayer. Hanneman contributed both lyrical and musical material to every Slayer album and wrote the songs "Raining Blood", "War Ensemble," "South of Heaven," "Seasons in the Abyss," and "Angel of Death," all of which have been played at almost every live Slayer performance after their respective compositions. He had his own signature guitar, the ESP Jeff Hanneman Signature model.
Document 14: Geezer Butler: Terence Michael Joseph "Geezer" Butler (born 17 July 1949) is an English musician and songwriter. Butler is best known as the bassist and primary lyricist of the heavy metal band Black Sabbath. He has also recorded with Heaven & Hell, GZR, and Ozzy Osbourne.
Document 15: Mike Ness: Michael James Ness (born April 3, 1962) is an American guitarist, vocalist, producer and chief songwriter for the punk rock band Social Distortion, which was formed in 1978. Mike Ness' songs are represented by Downtown Music Publishing.
ground_truth: vocalist