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Suppose i is such that Ai is infinite. Then, for every  s  with 0259-001.gif there are infinitely many 0259-002.gif such that 0259-003.gif.
Therefore, we have that
Ai is finite Image-2614.gif
0259-004.gif
0259-005.gif
0259-006.gif
So, 0259-007.gif, a contradiction.
§11.5 Bibliographic Notes
The study of function identification in the presence of membership oracles was initiated by Gasarch and Pleszkoch [76]. An earlier work in this direction is due to Adleman and Blum [1]. The reader is referred to a comprehensive paper by Fortnow, Gasarch, Jain, Kinber, Kummer, Kurtz, Pleszkoch, Slaman, Solovay, and Stephan [59] for numerous results on this topic.
The investigation of language identification in the presence of membership oracles was first considered by Jain and Sharma [87], and extended by Kummer and Stephan [114]. Ott and Stephan [146] demonstrate the use of oracles in the context of a model for learning infinite recursive branches of recursive trees due to Kummer and Ott [113].
A related model studied by Gasarch and Smith [77] allows a scientist to ask a teacher questions, phrased in a prespecified first-order language, about the function being identified.
§11.6 Exercises
11-1 (Adleman and Blum [1]) Suppose A is high (see page 253). Show that 0259-008.gif.
11-2 (Gasarch and Pleszkoch [76]) A set A is said to be low if 0259-009.gif. Show that 0259-010.gif.

 
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