**5.1.2 Mirror phenomenon**

During the evolution it was observed that after positive vortices joined (Fig.4(c, d)) the new big positive vortex acted as a moving wall for the negative vortex injecting vorticity to it. Reproducing the behavior seen in the square cavity, now by the negatie vortex. Ergo a *quasi square cavity* was created in the top of the cavity but instead having a moving wall it had a vortex. The phenomenon is shown in Fig.5 where it is clear that the top of the deep cavity is a "reflection" of the square cavity with respect to an imaginary vertical axis drawn between these two.
