A historian, physicist and mathematician were travelling by train from England to Scotland for the first time and as they crossed the border they saw a black sh

A historian, physicist and mathematician were travelling by train from England to Scotland for the first time and as they crossed the border they saw a black sheep. "Look!" said the historian, "Sheep in Scotland are black!" "No," said the physicist, "At least one sheep in Scotland is black." "Hmm." said the mathematician. "Of all the sheep in Scotland, at least one of them is at least half black."