A presentation of a finitely generated submonoid of invertible endomorphisms of the free monoid
نویسندگان
چکیده
An endomorphism of the free monoid A∗ is invertible if it is injective and extends to an automorphism of the free group generated by A. A simple example: the endomorphism that leaves all generators A invariant except one, say a, which is mapped to ba for some other generator b. We give a monoid presentation for the submonoid generated by all such endomorphisms when a and b are taken arbitrarily. These left translations are a special case of Nielsen positive transformations: “left” because the mutiplicative constant acts on the left and “positive” because this constant belongs to the free monoid, not the free group.
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