We discuss conditions necessary for appearance and discovery of the symbiotic star phenomenon within the model of a binary consisting of a red (super)giant 3 M G not filling the Roche lobe and of an accreting hot degenerate CO-dwarf 0.8 H Q . Within this model "classical" symbiotic stars may exist only within a narrow region of mass accretion rates and separations of components: 1CT* £ M
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