Viability problems arise in several scientific fields (robotics, economics, environmental sciences). Once the set of constraints to be satisfied is specified and the dynamics described, the viability problem is the study of the compatibility between these constraints and these dynamics; Control strategies governing viable evolutions if any can then be deduced.
Analytical solutions to sustainability problems are very rare. Approximations can then be calculated, we call them Viable Numerical Objects.
You can get further informations about Vino on this wiki.