Do All MSK-Type Signaling Waveforms Have Wider Spectra Than Those for PSK?

For all MSK-type signals proposed until now, the main lobes of their power spectral densities were observed to be always wider than those for conventional PSK. Although it is intuitively believed that this observation can be extended to cover all other MSK-type signals not yet found, no formal proof has been reported yet. The present paper attempts to give such a proof.