Given a set in a Banach space , we define: the tangent set, and the quasi-tangent set to at , concepts more general than the one of tangent vector introduced by Bouligand (1930) and Severi (1931). Both notions prove very suitable in the study of viability problems referring to differential inclusions. Namely, we establish several new necessary, and even necessary and sufficient conditions for viability referring to both differential inclusions and semilinear evolution inclusions, conditions expressed in terms of the tangency concepts introduced.

RESUMEN

We performed an asymptotic linear stability analysis of the static spike autosolitons (ASs)---self-sustained solitary inhomogeneous states---in the Gray--Scott model of an autocatalytic chemical reaction. We found that in one dimension these ASs destabilize with respect to pulsations or the onset of traveling motion when the inhibitor is slow enough. In higher dimensions, the one-dimensional static spike ASs are always unstable with respect to corrugation and wriggling. The higher-dimensional radially symmetric static spike ASs may destabilize with respect to the radially nonsymmetric fluctuations leading to their splitting when the inhibitor is fast or with respect to pulsations when the inhibitor is slow.