The F# compiler doesn't let me define a property which in C# would be written as:

```c#
public ISpecimenBuilder Relay
{
    get { return this.relay; }
}
```
AFAICT, in F#, explicit object constructors can only initialize *fields* of an object..

However this field is immutable and also the compiler emits a read-only property as shown in Reflector:

![image](https://f.cloud.github.com/assets/287532/1120949/a17ab5e4-1ab3-11e3-9526-2e106803a93b.png)

So perhaps we could keep it as-is?