Mishna Shevuot 4:13, towards end of mishna, explains that if someone says "May God not strike you if you testify on my behalf", Rabbi Meir deems him liable for cursing someone, because, according to Bartenura, he holds by "we learn yes from no", i.e. a negative statement of "don't be struck if you testify" implies the positive counterpart i.e. one should be struck if they don't testify, i.e. a curse, and this mishna is teaching us that curses are punishable.
בכל אלו ר״מ מחייב, דמכלל לאו אתה שומע הן
In all these cases, Rabbi Meir holds liable because he holds that we can learn yes from no
However, I find this Bartenura hard to understand, because the gemara he quotes actually has Rabbi Meir holding the exact opposite:
רַבִּי מֵאִיר — לֵית לֵיהּ מִכְּלָל לָאו אַתָּה שׁוֹמֵעַ הֵן
Rabbi Meir does not hold that we can learn yes from no
How do we understand the Bartenura? If the Barternura is a mistake, then what is the reason Rabbi Meir holds that such a person is liable in our mishna?