Difference between an engineer, physicist and a mathematician

An engineer, a physicist and a mathematician take a train ride through the Scottish countryside. Suddenly they see a sheep outside in a meadow.

The engineer says: "Wow, in Scotland all sheep are black!"

The physicist replies: "Not really; there is at least one black sheep in Scotland!"

The mathematician smiles and replies: "There is at least one sheep in Scotland with at least one black side."

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[Disclaimer : The blog text are contents as received in forwarded mails. Its nothing to do with my view or concerns]