–, –, +, –, –, +, –, …
The common pattern of Covid-19 test results of most air travelers: tested negative pre-departure and again negative on arrival at their destination, but later tested positive (with zero symptoms) while serving their quarantine at home or in a hotel.
A grade one math question is: “In the corona test series –, –, +, –, –, +, –, …, what are the signs of the next two terms?”