Given the following context:  "Single Ladies (Put a Ring on It)" was written by Beyoncé, Terius "The-Dream" Nash, Thaddis "Kuk" Harrell, and Christopher "Tricky" Stewart, and was produced by Nash and Stewart. Beyoncé recorded the song in May 2008 at the Boom Boom Room Studio in Burbank, California, and it was mixed by Jaycen Joshua and Dave Pensado, with assistance from Randy Urbanski and Andrew Wuepper. Nash conceptualized "Single Ladies" after Beyoncé's secret marriage to hip hop recording artist Jay-Z in April 2008. Stewart commented that the song was "the only public statement that [Beyoncé and Jay-Z had] ever made about marriage", and that while in the studio recording the song Beyoncé had remained tightlipped, even to the point of removing her wedding band. Beyoncé's marriage inspired Nash to compose a song about an issue that affected many people's relationships: the fear or unwillingness of men to commit. In an interview with Billboard magazine, Beyoncé added that she was drawn to the song because of the universality of the topic, an issue that "people are passionate about and want to talk about and debate". She stated that although "Single Ladies" is a playful uptempo song, it addresses an issue that women experience every day.In "Single Ladies", Beyoncé portrays her alter ego Sasha Fierce, which appears on the second part of I Am... Sasha Fierce. The song was released simultaneously with "If I Were a Boy"; as lead singles, they were meant to demonstrate the concept of the dueling personalities of the singer. This reinforced the theme of the album, which was created by placing its ballads and uptempo tracks on separate discs. The singles debuted on US radio on October 8, 2008; "Single Ladies" did so on mainstream urban New York radio station Power 105.1. Both singles were added to rhythmic contemporary radio playlists on October 12, 2008; "Single Ladies" was sent to urban contemporary playlists the same day, while "If I Were a Boy" was instead classified for contemporary hit radio. The two songs were released as a double A-side...  answer the following question:  Whose songs were meant to demonstrate the concept of the dueling personalities?
The answer to this question is:
Beyoncé