“…Focusing on neo-Hookean solids (2.23) they showed that the critical stretches are λ cr = 0.666 for tangential equibiaxial compression (λ 1 = λ, λ 2 = λ −2 , λ 3 = λ), λ cr = 0.544 for plane strain compression (λ 1 = λ, λ 2 = λ −1 , λ 3 = 1), and λ cr = 0.444 for normal equibiaxial compression (λ 1 = λ, λ 2 = λ −1/2 , λ 3 = λ −1/2 ). Theirs was a static stability analysis, later also included in a wider dynamical context by Flavin [28], Willson [29], Chadwick and Jarvis [30], Dowaikh and Ogden [12], and , where σ 0 is the real root of σ 3 + σ 2 + 3σ − 1 = 0 (σ 0 = 0.2956). Clearly, in the examples of plane strain and equi-biaxial strain above, the squared wave speed increases when λ increases and decreases when λ decreases.…”