Groups, fields and rings and everything!

So... what *if* instead of concrete values, we could have elements of groups, fields and rings? Like
```
public abstract class Group
{
public abstract ElementOfRing Add(ElementOfRing left, ElementOfRing right);
public abstract Zero();
// etc
}
```

```cs
public abstract class Ring : Group
{
public abstract ElementOfRing Multiply(ElementOfRing left, ElementOfRing right);
// etc
}
```

```cs
public abstract class Field : Ring
{
}
```

```cs
public abstract class ElementOfRing
{
// etc
}
```

And for sample, there will be

```cs
public static ElementOfRing Multiply(ElementOfGroup a, ElementOfGroup b)
=> (a, b) switch
{
(ElementOfField ea, ElementOfField eb) => field.Add(ea, eb)
_ => ...
}
```

There should be definitely more thoughts on it. We need to check how, say, SymPy does it.