A small practical task from everyday activities. There is a pharmacy. The light has disappeared for six months. And it disappears at a fixed time: around 8:00 and around 10:00. After a tumultuous discussion with our colleagues, we became proud of the man who connected this building to the power grid. Because he connected it to street lighting and turning off the light in the morning and turning it on in the evening led to turning off the light in the building.