```
struct Matrix(S, size_t M, size_t N)
{
}
alias Vec3(S) = Matrix!(S, 3, 1);
void main()
{
import std.stdio;
writeln(is(Vec3!float == Matrix!(S, 3, 1), S)); // `alias` `S` is defined here
writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S)); // Error: declaration `S` is already defined
}
```

Even though the following code compiles.

```
writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
```