In other words, because the singly occupied orbital space (see Figure ) is well defined by the choice of the high-spin reference, one can develop an effective truncation scheme of the rest of the virtual space based on the FNOs defined by the reference-state density matrix. Here we develop this idea into a practical algorithm of virtual space truncation by using singular value decomposition (SVD) procedure and illustrate the performance of the resulting method by calculations of multiple electronic states and interstate properties in selected diradicals and triradicals. We note that although EOM-SF-CC is a single-reference method and does not employ active spaces, the singly occupied orbital space defined by our procedure is conceptually similar to an active space of strongly correlated orbitals used within multi-reference formalisms . The utility of natural orbitals computed for high-spin states in multi-reference calculations of ground and low-lying excited states has been successfully exploited by Lu and Matsika.