(* Autor(s): Andrej Dudenhefner (1) Affiliation(s): (1) Saarland University, Saarbrücken, Germany *)
(* Undecidability Result(s): Simple Semi-unification (SSemiU) Right-uniform Two-inequality Semi-unification (RU2SemiU) Left-uniform Two-inequality Semi-unification (LU2SemiU) Semi-unification (SemiU) *)
(* Literature: [1] Andrej Dudenhefner. "Undecidability of Semi-Unification on a Napkin" 5th International Conference on Formal Structures for Computation and Deduction (FSCD 2020): 9:1-9:16 https://drops.dagstuhl.de/opus/volltexte/2020/12331 *)
Require Undecidability.SemiUnification.Reductions.CSSM_UB_to_SSemiU.
Require Undecidability.SemiUnification.Reductions.SSemiU_to_RU2SemiU.
Require Undecidability.SemiUnification.Reductions.RU2SemiU_to_LU2SemiU.
Require Undecidability.SemiUnification.Reductions.RU2SemiU_to_SemiU.
Check SSemiU_undec.
Check RU2SemiU_undec.

(* Undecidability of Left-uniform Two-inequality Semi-unification *)
Theorem LU2SemiU_undec : undecidable LU2SemiU.