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select distinct X, Y
from Functions func_a
where
(X = Y and (select count(func_b.X) from Functions func_b where func_a.X = func_b.Y and func_a.Y = func_b.X) > 1)
or
(X < Y and (select count(func_b.X) from Functions func_b where func_a.X = func_b.Y and func_a.Y = func_b.X) > 0)
order by X, Y;