linker error

[lodo]

When I try to compile the code below I get this error:
 prova00.obj(prova00)
 Error 42: Symbol Undefined _D6prova013implementThisFZi
 --errorlevel 1

This is my code:

File prova0.d:
import std.stdio;
int implementThis();
void callThis()
{
        writefln("%d",implementThis());
}

File prova00.d:
import prova0;
int implementThis()
{
        return 42;
}
void main()
{
        callThis();
}

Can someone help me, please?