An apple a day is an apple such that, if (x1, y1, z1) is your location on earth, then
sqrt[ (x2 – x1)^2 + (y2 – y1)^2 + (z2 – z1)^2 ] > M
where (x2, y2, z2) is the position of your doctor and where M is a real number of non-negligible quantity such that M > the distance your doctor would need to be around you to treat or examine you.
Optimal thought and optimal fitness through reason, logic, science, passion, and wisdom.