A simple algorithm for in-place merging

The early algorithms for in-place merging were mainly focused on the time complexity, whereas their structures themselves were ignored. Most of them therefore are elusive and of only theoretical significance. For this reason, the paper simplifies the unstable in-place merge by Geffert et al. [V. Geffert, J. Katajainen, T. Pasanen, Asymptotically efficient in-place merging, Theoret. Comput. Sci. 237 (2000) 159-181]. The simplified algorithm is simple yet practical, and has a small time complexity.