Why is the â with a circumflex in this sentence? I would expect it to be a normal a?
"a" means and, "â" is a preposition. "Peidio" is always followed by "â" if the following word begins with a consonant or "ag" if the following word begins with a vowel.
In the big Welsh challenge they leave the â out here (peidio mynd). Is there a difference between both constructions, register or something?
It's mostly left out in spoken Welsh. The person who wrote this section was in a school where they teach it, in Welsh for adults classes it's left out.
In the Duolingo course it's marked correct either way.