Rasiowa-Sikorski proof system for the non-Fregean sentential logic SCI

The non-Fregean logic SCI is obtained from the classical sentential calculus byadding a new identity connective ≡ and axioms which say ‘α ≡ β’ means ‘α is identicalto β’. We present complete and sound proof system for SCI in the style of Rasiowa-Sikorski.It provides a natural deduction-style method of reasoning for the non-Fregean sentential logicSCI.