Statically matching constraints

I'm having a bit of trouble understanding the "both are nonstatic and
result from..." clause of 4.9.1(1.3/2). According to 7.3(13), if you
have a discriminant on the ancestor subtype of a private extension,
the full definition must impose a statically matching constraint,
which takes you to 4.9.1. With this in mind, which of these examples
is legal?

package Pak1 is
X : Integer := 3;
type T1 (A : Integer) is tagged null record;
type T2 is new T1(X) with private;
private
type T2 is new T1(X) with null record;
end Pak1;

package Pak2 is
X : constant Integer := Some_Other_Package.Some_Function(100);
type T1 (A : Integer) is tagged null record;
type T2 is new T1(X) with private;
private
type T2 is new T1(X) with null record;
end Pak2;

package Pak3 is
X : Integer := 3;
type Sub is Integer range 1..X;
type T1 (A : Integer) is tagged null record;
type T2 is new T1(Sub'Last) with private;
private
type T2 is new T1(Sub'Last) with null record;
end Pak3;

My reading is that Pak1 and Pak2 are illegal but Pak3 seems to be
legal. The constraints are all nonstatic (the fact that X is a
constant in Pak2 isn't enough to make it static), but it seems to me
that Pak3 is the only one where the constraint results from something
mentioned in 4.9.1(1.3/2), since it seems to result from "the same
evaluation of a range of a discrete_subtype_definition", while in Pak1
and Pak2 the constraints result from evaluations of a variable or
constant, respectively. But it's a little confusing to me because I'm
not clear on just what "result from" is supposed to mean, and the AARM
is no help.

Is my interpretation correct?

(And yes, I already know you can make this legal by eliminating the
discriminant from the private extension declaration. That isn't my
question.)

-- thanks, Adam

.

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