What's the negation of “At least three of the sentence are false”? Following with the question I asked before

What&#39;s the negation of &quot;One of the sentence is false&quot;?

The negation of “At least three of the sentence are false” would be "any, one or two of the sentence is/are false"?
Call $f$ the number of false sentences.
Your "At least $3$ of these sentences are false" is 
$$
f \ge 3
$$
The negation of this is clearly
$$ f &lt; 3$$
Thus, "the number of false sentences is smaller than $3$", i.e., "there are $0$, $1$ or $2$ false sentences", i.e., "there are at most $2$ false sentences."
No! The negation of the sentence "At least one of the three sentences is false" is "All three of the sentences are true" or, equivalently "None of the sentences are false".