Summary. We investigate the second order bounded arithmetical systems which is isomorphic to TAC ~, TNC i or TLS.In [1], S. Buss has introduced the first order systems of Bounded Arithmetic S~ and T~, which corresponds to computational classes in polynomial hierachy A~' and AiP+I respectively. Especially S~ corresponds to the polynomial time computable class P. There he has also introduced a bounded second order system U~(BD) which corresponds to the computational class PSPACE.There are many important computational classes below P e.g. AC i, NC i, and L. The classes NC i and AC' are those predicates or functions computable by a uniform family of polynomial size, O(log i n) depth circuits with constant and unbounded fanin respectively. The class L is those predicates or functions logspace computable by a deterministic Turing machine.In Clote and Takeuti
MSP(a,i + l)= llMSP(a,i) j •In order to formulate these theories the notion "essentially sharply bounded" (abbreviated by esb) plays a central role. Let T be a theory in Bounded Arithmetic. A formula is said to be esb in T if it belongs to the smallest family ._~7" satisfying the following conditions.(1) Every atomic formula belongs to ~° (2) ~ is closed under Boolean connectives.(3) ~" is closed under sharply bounded quantifications.