[Haskell-beginners] fixpoint operator for ULC with specific reduction property

[ben]

Hello,

I'm looking for a fixpoint operator Z for the untyped lambda calculus
that has the property

Z g --> g (Z g)

for any g.

The best-known fixpoint operator Y := \f. (\x. f (x x)) (\x. f (x x))
does not have this property, but only

Y g --> T <-- g (Y g)

for some T.

Does anybody know such a Z I'm looking for?

Greetings,
ben

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