Question: In what year was the heavy metal band from Tronheim, Norway, who specializes in music that embodies a continuous move between explicit and implicit references to genres and strategies derived from cultural domains, formed?

Context articles: Toxicity (album)
Progressive music
Australian heavy metal
Nu metal
Kekal
Heavy metal lyrics
Heavy metal bass
Tulikoira
Darkthrone
Triosphere

Toxicity is the second studio album by the Armenian-American heavy metal band System of a Down, released on September 4, 2001 by Columbia Records.
 Categorized as alternative metal, thrash metal, hard rock, art metal, heavy metal, and nu metal, "Toxicity" features elements of multiple genres of music: folk, progressive metal, progressive rock, jazz, Middle Eastern music, and Greek music.
 Many of the album's lyrics are political, being about topics such as the overpopulation of prisons, the CIA, and Charles Manson's beliefs about the environment.
 Examples of non-political themes in "Toxicity"'s lyrics are group sex, drug addiction, and groupies.
Progressive music is music that subverts genre and expands stylistic boundaries outwards.
 Rooted in the idea of a cultural alternative, musical progressiveness embodies a continuous move between explicit and implicit references to genres and strategies derived from various cultural domains, such as European art music, Celtic folk, West Indian, or African.
 The word "progressive" comes from the basic concept of "progress", which refers to development and growth by accumulation, and is often deployed in numerous music genres such as progressive country, progressive folk, progressive jazz, and (most significantly) progressive rock.
Australian heavy metal music has its roots in both the Australian hard rock and pub rock tradition of the 1970s and the American and British heavy metal scenes.
 Since the mid-1980s, Australian heavy metal has been particularly influenced by foreign bands, particularly Swedish death metal, American thrash metal and black metal from Norway.
 Within Australia heavy metal has always remained part of the underground but since the mid-1990s many Australian metal acts have found widespread acceptance in overseas markets, particularly in Europe.
Nu metal (also known as nü-metal and aggro-metal ) is a form of alternative metal that combines elements of heavy metal music with elements of other music genres such as hip hop, alternative rock, funk and grunge.
 Nu metal bands have drawn elements and influences from a variety of musical styles, including multiple genres of heavy metal.
 Nu metal rarely features guitar solos; the genre is heavily syncopated and based on guitar riffs.
 Many nu metal guitarists use seven-string guitars that are down-tuned to play a heavier sound.
 DJs are occasionally featured in nu metal to provide instrumentation such as sampling, turntable scratching and electronic backgrounds.
 Vocal styles in nu metal include singing, rapping, screaming and growling.
 Nu metal is one of the key genres of the new wave of American heavy metal.
Kekal (sometimes stylized as KEKAL) is a heavy metal and electronic music band formed in 1995 in Jakarta, Indonesia.
 According to AllMusic, Kekal was one of the first heavy metal bands from Indonesia to make international inroads, and according to sociologist of heavy metal, Keith Kahn-Harris, was one of the few extreme metal bands from Southeast Asia to ever make more than a minimal impression on the global scene.
 Founded by two musicians known simply Yeris and Newbabe, the band underwent some shifts in lineup in its early years, but emerged with a consistent lineup of three key-members, guitarist/vocalist Jeff Arwadi, bassist Azhar Levi Sianturi, and guitarist Leo Setiawan.
 Frequently labeled as black metal, progressive metal, and avant-garde metal, Kekal plays a very diverse range of music styles within the frame of metal and rock, incorporating many other music genres such as ambient, electronic, jazz fusion, and progressive rock.
 Over the course of its career, Kekal has transitioned from a heavy metal-based style to a more experimental and electronic sound.
Heavy metal lyrics are the words used in songs by heavy metal artists.
 Given that there are many genres of heavy metal, it is difficult to make generalizations about the lyrics and lyrical themes.
 In 1989, two metal scholars wrote that heavy metal lyrics concentrate "on dark and depressing subject matter to an extent hitherto unprecedented" in any form of popular music.
 Jeffrey Arnett states that metal songs are "overwhelmingly dominated" by "ugly and unhappy" themes which express "no hope" for the future.
 Deena Weinstein has proposed one way to analyze metal song themes is loosely grouping them into two categories: the Dionysian theme (a reference to the Roman God of wine), which celebrates "sex, drugs and rock and roll", partying, and enjoyment of life and the Chaotic theme, which involves dark subjects such as Hell, injustice, mayhem, carnage and death.
 Not all metal genres fall into Weinstein's two theme model; for example power metal's lyrical themes often focus on fantasy and mythology, camaraderie and hope, personal struggles and emotions, among other themes.
 Another exception is pop metal bands, which replaced "gloom and doom" themes with "positive, upbeat" songs about romantic love and relationships, part of their goal of appealing more to female listeners.
 In metal overall, the small number of metal songs about relationships are typically about unions that have "gone sour" long ago.
Heavy metal bass is the use of the bass guitar (also called "electric bass") in the rock music genres of heavy metal and hard rock.
 The bassist is part of the rhythm section in a heavy metal band, along with the drummer, rhythm guitarist and, in some bands, a keyboard player.
 The prominent role of the bass is key to the metal sound, and the interplay of bass and distorted electric guitar is a central element of metal.
 The bass guitar provides the low-end sound crucial to making the music "heavy".
 The bass plays a "...more important role in heavy metal than in any other genre of rock."
Tulikoira is the nineteenth album recorded by the Finnish experimental rock band Circle.
 Released on CD in 2005 by Ektro Records, the album has the band incorporating elements of both drone music and black metal into the krautrock sound of previous albums like "Prospekt".
 Proclaiming themselves the "New Wave of Finnish Heavy Metal", in honour of the new wave of British heavy metal movement, Circle here made explicit their long-held love of 1970s and 1980s heavy metal music.
 A re-release by Headspin Records in 2007 has a bonus 7" containing material from the band's "Earthworm" EP recorded with the American singer Bruce Duff.
 Both songs were re-released on the 2008 album "Hollywood" which also has Duff on vocals.
Darkthrone is a Norwegian heavy metal band.
 It formed in 1986 as a death metal band under the name Black Death.
 In 1991, the band embraced a black metal style influenced by Bathory and Celtic Frost and became one of the leading bands in the Norwegian black metal scene.
 Their first three black metal albums—"A Blaze in the Northern Sky", "Under a Funeral Moon" and "Transilvanian Hunger" (sometimes dubbed the "Unholy Trinity") — are considered the peak of the band's career and to be among the most influential albums in the genre.
 For most of this time, Darkthrone has been a duo of Nocturno Culto and Fenriz, who have sought to remain outside the music mainstream.
 Since 2006, their work has strayed from the traditional black metal style and incorporated more elements of traditional heavy metal, speed metal and punk rock, being likened to Motörhead.
Triosphere is a Norwegian heavy metal band from Trondheim, Norway, created in 2004 by singer and bassist Ida Haukland, and guitarist Marius Silver Bergesen.
 They are defined by their heavy metal sound emphasising their power metal-like melodies and choruses, while also featuring progressive elements.
 Bergesen is the composer of all instrumental parts, with Haukland acting as lyricist, and composer of the vocal parts.