Christian Mathissen. Existential MSO over two successors is strictly weaker than over linear orders. Theoretical Computer Science, 410(38-40):3982-3987, 2009. [doi]
@article{Mathissen09,
title = {Existential MSO over two successors is strictly weaker than over linear orders},
author = {Christian Mathissen},
year = {2009},
doi = {10.1016/j.tcs.2009.04.019},
url = {http://dx.doi.org/10.1016/j.tcs.2009.04.019},
researchr = {https://researchr.org/publication/Mathissen09},
cites = {0},
citedby = {0},
journal = {Theoretical Computer Science},
volume = {410},
number = {38-40},
pages = {3982-3987},
}