“For example, in the chorus of Mos Def's "Mathematics," Premier cuts the following in quick succession:

• "The Mighty Mos Def" (from Mos Def's "Body Rock"),
• "It's simple mathematics" (from Fat Joe's "John Blaze"),
• "Check it out" (Lady of Rage from Snoop Dogg's "For All My Niggaz & Bitches"),
• "I revolve around science" (from Ghostface Killah's verse on Raekwon's "Criminology"),
• "What are we talking about here" (from the movie "Ghostbusters"),
• "Do your math" (from Erykah Badu's "On & On"), and
• "One, two, three, four" (from James Brown's "Funky Drummer")

On certain artists' work the vocal samples will all be vocal samples of the artist from the artist's past work; "Nas Is Like" and Nas' "2nd Childhood" are two well-known examples of this.”

— DJ Premier - Wikipedia

Interesting to see where those cuts comes from... one of Mos Def's best.