Structured decomposition for reversible Boolean functions.

We give a structured decomposition for reversible Boolean functions. Specifically, an arbitrary n-bit reversible Boolean function is decomposed to 7 blocks of (n-1)-bit Boolean function, where 7 is a constant independent of n; and the positions of those blocks have large degree of freedom. Our result improves Selinger's work by reducing the constant from 9 to 7 and providing more candidates when choosing positions of blocks.