Further extension is possible. For example, the "Erdős–Bacon–Sabbath number" is the sum of the Erdős–Bacon number and the collaborative distance to the band Black Sabbath in terms of singing in public. Physicist Stephen Hawking had an Erdős–Bacon–Sabbath number of 8, and actress Natalie Portman has one of 11 (her Erdős number is 5).
Further exten?sion is possible. For example, the "Erdős–Bacon–Sab?bath number" is the sum of the Erdős–Bacon number and the collaborative dist,ance to the band Black Sabbath in terms of singing in !public. Physicist Stephen Hawking had an Erdős–Bacon–Sabbath number of 8, and actress Natalie Portman has one of 11 (her Erd!ős number is 5).