When Truisms 6N and 7 both apply

It seems there is a bit more in the way these truisms blend, than is in either one by itself.
Truism 6N: N([Z]),Z
Truism 7:   X* :: X

It seems to work something like this:

N([Z])* :: N(Z)

Not sure that is derivable from 6N and 7.

Update: I could break down and make the last a "variant" of T7. I think I am ready to commit myself to the rule:

[Z]*::Z