[Demo] Distinct denominators for 4/n

 on residue classes sometimes repeat a denominator. We show they can always be rearranged to use three different denominators when 

 already uses three different denominators when 

So whenever one of these identities applies, three different denominators are possible. For 

 they are not: three different unit fractions add up to at most 

A small result, but it came up in the Erdős–Straus project and we wanted it written down. The project notes stay private. The paper is public.

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