= Solution
Add a public override of `toString` in each concrete subclass. In `TypeVar`:
``
public String toString() {
return "t" + id.toString();
}
``
In `Arrow`:
``
public String toString() {
return "(" + from.toString() + " -> " + to.toString() + ")";
}
``
Inherited dynamic dispatch selects the proper method at every node of the <abstract syntax tree>. Full parentheses distinguish the domain and codomain nesting without relying on a reader's precedence convention. Repeated occurrences of one <type variable> use the same identifier, and distinct factory variables have distinct identifiers. For example, with the first three factory variables, the type from part (b) prints as `((t1 -> t2) -> (t2 -> t3))`. \b[The recursive textual form preserves both arrow structure and variable identity.]
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