Mappings with Coenumerable Graphs
摘要
We study partial mappings on natural numbers, the graphs of which are coenumerable. Such mappings are referred to as negative mappings. We show that any 0′-computable partial function is represented as the superposition of two negative ones. We also show that the inverse semigroup of all 0′-computable partial injective mappings is generated by its negative elements; moreover, any its element is equal to the product of its two negative elements. We show that the group of all 0′-computable permutations is generated by its negative elements. We obtain sufficient conditions for the representability of 0′- computable permutations in the form of the superposition of two negative permutations.