Proof

At the Macmillan Dictionary, this week’s language tip is about countable and uncountable proof.

When proof means ‘information that proves something’, it is almost always an uncountable noun, and so:
       ▪  it rarely comes after a or a number
       ▪  it is rarely used in the plural
 
✗ The fact that science never stops developing is a proof that man never stops using his imagination.
✓ The fact that science never stops developing is proof that man never stops using his imagination.
✗ There are no proofs that homosexual couples are not able to bring up healthy, stable children.
✓ There is no proof that homosexual couples are not able to bring up healthy, stable children.
 
The countable noun proof (usually found in the plural) is a technical word for a copy of a book or article which has to be checked before being printed:
The corrected proofs have been delivered to the printer.