The symbol which is not used very commonly in mathematics. The double dagger is also known as the double obelisk or diesis (Bringhurst 1997, p. 275).

Bringhurst, R. The Elements of Typographic Style, 2nd ed. Point Roberts, WA: Hartley and Marks, p. 277, 1997.

CITE THIS AS:

Weisstein, Eric W. "Double Dagger." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/DoubleDagger.html