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Constructive proofs of the range property in lambda calculus. (English) Zbl 0796.03020
The range property, conjectured in 1968 by Böhm, says that the range of a combinator $$F$$, that is the set of all terms $$F A$$ modulo $$\beta$$- convertibility, is either a singleton or an infinite set. This paper recalls first the classical (nonconstructive) proofs and then gives two constructive proofs. The first one adds to Böhm’s idea of using a fixed point the coding of lambda-terms by natural numbers. The second is based on Ershov numerations. This leads to a generalization of the range theorem due to Statman.

##### MSC:
 03B40 Combinatory logic and lambda calculus 03D45 Theory of numerations, effectively presented structures
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##### References:
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