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THE JOURNAL or SYMBOLIC LOGIC Volume 14, 2, June 1949

DEFINABILITY AND DECISION PROBLEMS IN

JULIA ROBINSON Introduction. In this paper, we are concerned with the arithmetical defin­ ability of certain notions of and rationals in terms of other notions. The results derived will be applied to obtain a negative solution of corresponding decision problems.1 In Section 1, we show that of positive integers can be defined arith­ metically in terms of and the unary of successor