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- What is a proof? 14 answers
What exactly is a mathetmatical proof? From this question it's clear it doesn't require any special symbols.
[Computer] Viruses have no “cure.” It’s been mathematically proven that it is always possible to write a virus that any existing antivirus program can’t stop." 
 Secrets & Lies. Bruce Schneier. Page 154
In these contexts what does it even mean to be mathematically proven? Does it just mean logic was used?