The derivative of a quintic function is a quartic function. Moreover, it shows that quintic equations are algebraically unsolvable. An algorithm is also available for monotone quintic Hermite interpolation. These include the quintic equations defined by a polynomial that is reducible, such as . This is one of the simplest examples of a non-solvable quintic polynomial. Watson's interests included solvable cases of the quintic equation. "Casus irreducibilis" for quintic polynomials is discussed by Dummit. For example, consider the nonsingular quintic threefold in formula 127. Nevertheless, the modern methods for solving solvable quintic equations are mainly based on Lagrange's method. In other words, a quintic function is defined by a polynomial of degree five. See quintic equation, sextic equation, and septic equation. Some quintic equations can be solved in terms of radicals. During that time, Abel started working on the quintic equation in radicals. The development partnership between Quintic and Computervision transferred to PTC. The development partnership with Quintic also transferred.