A hierarchy for nondeterministic time complexity

Stephen A. Cook
1973 Journal of computer and system sciences (Print)  
We prove the following theorem in this paper: For any real numbers rl, r2, 1 ~ rl ~ r2, there is a set .4 of strings which has nondeterministic time complexity n*2, but not nondeterministic time complexity n*l. The computing devices are nondeterministic multitape Turing machines.
doi:10.1016/s0022-0000(73)80028-5 fatcat:4errebavb5hirb4rnywcso3ygy