How functions propagate recommendations

For brevity, let's define Pair := Cons<String_Positive>.

An important piece of this puzzle is determining how the top-level cons knows what recommendations to pass to its children. The trick is to construct a function type representing the current invocation of cons, and compare it to the actual type of the cons function.
Since the invocation of cons is called with 2 arguments, and is recommended to return List<Pair>, we construct the type &(ARG1 ARG2) -> List<Pair>. Compare this to the real type-signature of cons:

invocation: &(ARG1 ARG2) -> List<Pair>
cons: &(A B) -> ConsFresh<A_B>

Attempting to match ConsFresh<A_B> against List<Pair> gets us the following:

ConsFresh<A_B> <: List<Pair>
A <: Pair
B <: List<Pair>

Then, we attempt to match the invocation arglist to the function arglist:

&(ARG1 ARG2) = &(A=Pair B=List<Pair>)
ARG1 = Pair
ARG2 = List<Pair>

Thus, we determine argument 1 — (cons "Alice" 1.5) — should get the recommendation Pair, and that argument 2 — nil — should get the recommendation List<Pair>.