Compilation Issue Due to Method Definitions in Both '.cpp' and '.hpp' Files in 'greg_weekday' Class

The methods in the **"greg_weekday"** class are defined in both the **.cpp and .hpp** files, which causes a compilation issue.

For example, the **as_short_string** method is defined in **greg_weekday.cpp** as follows:

```cpp
//! Return a 3-digit English string of the day of the week (e.g., Sun)
const char* greg_weekday::as_short_string() const
{
return short_weekday_names[value_];
}
```

However, the same method is also defined in the **.hpp** file as:

```cpp
//! Return a 3-digit English string of the day of the week (e.g., Sun)
const char* as_short_string() const
{
static const char* const short_weekday_names[]
= {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};

return short_weekday_names[value_];
}
```