Third person singular present: helps or provides assistance together with another person.
From 'coassist' plus the third person singular suffix '-s,' which marks present tense actions done by he/she/it. Standard English conjugation pattern.
English only adds '-s' for third person singular in the present tense (he runs, she jumps, it works), which is why I say 'I run' but 'she runs'—a quirk we inherit from Old English!
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