An inner model is projectively well-ordered when there is a projective relation that well-orders the real numbers belonging to .
For an inner model , the ordinal is the least ordinal that regards as uncountable. Equivalently, it is the supremum of the order types of the well-order codes belonging to . It can be countable in the ambient universe.
If is projectively well-ordered and projective determinacy holds, then is countable in the ambient universe. Otherwise, selecting with the projective well-order the least -code for each countable ordinal produces an uncountable projective set of unique well-order codes. It has no perfect subset by the boundedness theorem for well-order codes, contradicting the perfect set property implied by projective determinacy.
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