Kraaijevanger–MacDonald–Gottlieb conjecture on the radius of absolute monotonicity

Let $A,b$ denote the coefficients of an implicit Runge–Kutta method of order $p\ge 2$ with $s\ge 1$ stages. Its radius of absolute monotonicity is denoted by $R(A,b)$.

Kraaijevanger–MacDonald–Gottlieb conjecture. For every such method,

$$R(A,b)\le 2s.$$

This conjecture concerns the sharp upper bound for the strong-stability-preserving coefficient of implicit Runge–Kutta methods. The source states that it had previously been proved only for $s=1$ or $s=2$; its status here is recorded as resolved.