Black cows

    ​An engineer, a physicist and a pure mathematician see a black cow lying in a field shortly after crossing the English-Scottish border on a train.
    The engineer exclaims:" Look, Scottish cows are black!"
    The physicist replies: "No - some Scottish cows are black".
    The pure mathematician reacts with irritation:
    "There is at least one field, containing at least one cow, of which at least one side is black" she says.

    (Courtesy New Scientist Feedback, Oct. 31, 2020)