TOPOLOGICAL CHARGE OF ADHM INSTANTON ON ${\bf R}^2_{\rm NC}\times{\bf R}^2$.

We have calculated the topological charge of U(N) instantons on nondegenerate noncommutative spacetime to be exactly the instanton number k in a previous paper.1 This paper, which deals with the degenerate ${\bf R}^2_{\rm NC}\times{\bf R}^2$ case, is the continuation of Ref. 1. We find that the same conclusion holds in this case, thus complete the answer to the problem of topological charge of noncommutative U(N) instantons. [ABSTRACT FROM AUTHOR]