1. The tangent stiffness matrix is obtained from the engineering strain and the principle for determining the limit point and bifurcation point is given.

2. Compactness Characterization Theorem Suppose that K is a subset of a metric space X, then the following are equivalent: K is compact, K satisfies the Bolzanno-Weierstrass property (i.e., each infinite subset of K has a limit point in K), ; K is sequentially compact (i.e., each sequence from K has a subsequence that converges in K).