Question: Are Andrew Stockdale and Sully Erna both vocalists?

full_context: Document 1: Wolfmother: Wolfmother are an Australian hard rock band from Sydney, New South Wales. Formed in 2000 by vocalist and guitarist Andrew Stockdale, bassist and keyboardist Chris Ross and drummer Myles Heskett, the group currently includes Stockdale, bassist and keyboardist Ian Peres and drummer Hamish Rosser. Wolfmother released their self-titled debut album "Wolfmother" in Australia in 2005 and internationally in 2006. The album reached number 3 on the Australian Albums Chart and the top 40 in the US and the UK, and has to date sold over 1.5 million copies worldwide.
Document 2: Andrew Stockdale: Andrew James Stockdale (born 20 July 1976) is an Australian rock musician, singer and songwriter best known as the lead vocalist, lead guitarist and only mainstay member of the rock band Wolfmother, which formed in 2000. In 2007, alongside his Wolfmother bandmates, he won 'Songwriter of the Year' at the APRA Awards. Aside from his work with Wolfmother, Stockdale was featured on the 2010 single "By the Sword" by Slash.
Document 3: Sully Erna: Salvatore Paul "Sully" Erna Jr. (born February 7, 1968) is the American vocalist and guitarist for the American hard rock band Godsmack. He is also a harmonica player, percussionist and pianist, performing these on albums and at live shows. He was ranked 47th in the Top 100 Heavy Metal Vocalists by "Hit Parader".
Document 4: Tony Rombola: Tony Rombola (born November 24, 1964) is an American musician who has been the lead guitarist and backing vocalist for the Boston-based Hard Rock band Godsmack since the mid-1990s. Tony Rombola has been cited as 'an extraodinaire' in the guitar world, by Guitar World magazine, and is cited to be the only guitarist to keep an 'original soloing style' during the nu metal period, earning him the respect of the guitar industry. Rombola is also a guitarist for the side-project band Another Animal, formed at the beginning of 2007, the band released their self-titled debut album in October 2007, and played shows, whilst frontman Sully Erna did a small solo tour.
Document 5: List of songs recorded by Wolfmother: Wolfmother are an Australian hard rock band formed in Sydney, New South Wales in 2000. Originally a trio featuring vocalist and guitarist Andrew Stockdale, bassist and keyboardist Chris Ross, and drummer Myles Heskett, the group released their self-titled debut album in Australia in 2005, with all 12 tracks credited equally to all three band members. Four songs – "Dimension", "Woman", "White Unicorn" and "Apple Tree" – had originally been released on the band's self-titled debut EP the previous year. When "Wolfmother" was released internationally in 2006, it also featured "Love Train". In May 2007, the band contributed "Pleased to Meet You" to the "Spider-Man 3" soundtrack.
Document 6: Godsmack discography: Godsmack is an American alternative metal band founded in 1995 by singer Sully Erna and bassist Robbie Merrill. The band has released six studio albums, one EP, one compilation, three video albums, and twenty-three singles. Erna and Merrill recruited local friend and guitarist Lee Richards and drummer Tommy Stewart to complete the band's lineup. In 1996, Tony Rombola replaced Richards, as the band's guitarist. In 1998, Godsmack released their self-titled debut album, a remastered version of the "All Wound Up" demo. The album was distributed by Universal/Republic Records and shipped four million copies in the United States. In 2001, the band contributed the track "Why" to the Any Given Sunday soundtrack. After two years of touring, the band released "Awake". Although the album was a commercial success, it failed to match the sales of "Godsmack". In 2002, Stewart left the band due to personal differences, and was replaced by Shannon Larkin.
Document 7: Godsmack: Godsmack is an American rock band from Lawrence, Massachusetts, formed in 1995. The band is composed of founder, frontman and songwriter Sully Erna, guitarist Tony Rombola, bassist Robbie Merrill, and drummer Shannon Larkin. Since its formation, Godsmack has released six studio albums, one EP ("The Other Side"), four DVDs, one compilation album ("Good Times, Bad Times... Ten Years of Godsmack"), and one live album ("Live and Inspired").
Document 8: Tim Sult: Tim Sult is the guitarist for hard rock band Clutch. He is also the guitarist for an instrumental side project, The Bakerton Group, and an occasional member of the reggae rock / stoner rock band Lionize, as well as recently formed band Deep Swell. Sult has remained the guitarist for Clutch since the group started in 1990.
Document 9: Lisa Guyer: Lisa Guyer is an American singer, guitarist, and songwriter. She was born into a musical family that put on shows in their community, and Guyer learned to sing and dance by age four. Guyer's vocal skills are completely self-taught. Godsmack's Sully Erna describes Guyer as having "a phenomenal voice and a four-octave range. Guyer is an associate professor at Berklee College of Music in Boston.
Document 10: Keep Moving (Andrew Stockdale album): Keep Moving is the debut solo studio album by Australian hard rock musician Andrew Stockdale. Initially conceived as the third album by Stockdale's band Wolfmother, it was later announced to be a solo album after the disbandment of the group in March 2013. Recorded by Wolfmother between 2011 and 2013, "Keep Moving" was released by Universal in June 2013.
Document 11: By the Sword (song): "By the Sword" is the first official single from the album "Slash" by former Velvet Revolver and current Guns N' Roses lead guitarist Slash. It features Andrew Stockdale of Wolfmother on vocals and was released as a digital single on March 16, 2010. It was released in the UK on March 28, 2010. The cover was drawn by Ralph Steadman.
Document 12: Slash (musician): Saul Hudson (born July 23, 1965), better known by his stage name Slash, is a British-American musician and songwriter. He is best known as the lead guitarist of the American hard rock band Guns N' Roses, with whom he achieved worldwide success in the late 1980s and early 1990s. During his later years with Guns N' Roses, Slash formed the side project Slash's Snakepit. After leaving Guns N' Roses in 1996, he co-founded the supergroup Velvet Revolver, which re-established him as a mainstream performer in the mid to late 2000s. Slash has since released three solo albums: "Slash" (2010), featuring an array of famous guest musicians, and "Apocalyptic Love" (2012) and "World on Fire" (2014), recorded with his band, Myles Kennedy and the Conspirators. He returned to Guns N' Roses in 2016, nearly 20 years after he had left.
Document 13: List of Wolfmother members: Wolfmother are an Australian hard rock band from Sydney, New South Wales. Formed in 2000, the band originally included vocalist and guitarist Andrew Stockdale, bassist and keyboardist Chris Ross, and drummer Myles Heskett, the three of whom had been jamming together for a number of years before the band's first public performance in 2004. The group released their self-titled debut studio album "Wolfmother" in Australia in 2005, followed by international releases the following year, the songwriting for which was credited equally to all three band members. The founding lineup remained until August 2008, when Ross and Heskett left the band due to "irreconcilable personal and musical differences".
Document 14: Back Round: "Back Round" is a song by Australian hard rock band Wolfmother. Written by vocalist and guitarist Andrew Stockdale, the song was the first material released since original band members Chris Ross and Myles Heskett left the band in August 2008. "Back Round" was originally released as a free digital download on the band's official website on 30 March 2009, and was later released as a downloadable single on iTunes on 26 May 2009. In October 2009 the song was featured on the deluxe edition of the band's second album, "Cosmic Egg".
Document 15: Avalon (Sully Erna album): Avalon is the first solo studio album by American rock musician Sully Erna, released on September 14, 2010. "Avalon" is a combination of work that took Sully Erna almost seven years to complete.
ground_truth: yes