  Flexible systems are linear systems of inclusions in which the elements of
the coefficient matrix are external numbers in the sense of nonstandard
analysis. External numbers represent real numbers with small, individual error
terms. Using Gaussian elimination, a flexible system can be put into a
row-echelon form with increasing error terms at the right-hand side. Then
parameters are assigned to the error terms and the resulting system is solved
by common methods of linear algebra. The solution set may have indeterminacy
not only in terms of linear spaces, but also of modules. We determine maximal
robustness for flexible systems.
