Can't understand templates

[Sly via Digitalmars-d-learn]

Here is an example from the tutorial:

struct Point(T)
{
      T x;
      T y;
}

T getResponse(T)(string question) {
      writef("%s (%s): ", question, T.stringof);
      T response;
      readf(" %s", &response);
      return response;
}

Point!T getResponse(T: Point!T)(string question) {
      writefln("%s (Point!%s)", question, T.stringof);
      auto x = getResponse!T(" x");
      auto y = getResponse!T(" y");
      return Point!T(x, y);
}

void main()
{
      auto pt = getResponse!(Point!int)("point");
}


I don't understand how to read this signature: Point!T
getResponse(T: Point!T)(string question). Clearly it's not
supposed to be saying that T is subclass of Point!T, so those Ts
must refer to different types. But when I rename it to
getResponse(U: Point!T) I get a compilation error (unknown
identifier T).

Another question: say I have a template class Pair:

class Pair(A, B) {
      A a;
      B b;
      this(A a, B b) {this.a = a; this.b = b;}
}

How to write a specialization for getResponse matching Pair!(A,
B) with any type arguments A and B? I tried this:

T getResponse(T)(string question)
      if (is(T: Pair!(A, B), A, B))
{
      auto a = getResponse!A(" a");
      auto b = getResponse!B(" b");
      return new Pair!(A, B)(a, b);
}

but get a compile error:

error: d.getResponse called with argument types (string) matches
both:
        d.d(19): getResponse(T)(string question)
and:
        d.d(40): getResponse(T)(string question) if (is(T : Pair!(A, B),
A, B))