О биподобии в регулярном g-пространстве (полу) унитарного оператора гильбертого (полу) унитарному

(Semi)unitary operators on inner product spaces are studied. The conception of bisimilarity of operators on nondegenerated G-spaces is introduced. The criterion of bisimilarity in a regular G-space of a (semi)unitary operator to a (semi)unitary one in Hilbert sense is obtained by using results generalizing well-known Wold decomposition.