in the code that compensated for that. With that, things fell in place. I later visited Miloš just before his retirement from the Czech Academy of Sciences. When I described the problem to him, he said, of course, you are using the program to do things that it was not meant to do, and then proceeded to figure out what the real problem was.

After 2008, I was ready to use my new algorithms to do things, but did not have any good data to try them on. Before [*Kepler*]{}, TTVs were measured for hot Jupiters and alike, which do not have planetary companions too often. Also, companions would need to be fairly close or near resonant period ratios for the TTV method to work. In addition, the ground-based transit observations produced TTVs with rather large measurement errors and sparse transit coverage. That was not good enough for solving the inverse problem. I knew that well because I was experimenting on mock systems, where I would inject realistic measurement errors in the TTV data and vary the number of observed transits. It turns out that even for an excellent signal-to-noise (Kepler-46 has $S/N \sim 50$, where $S/N$ is defined here 