D import stmt doesn`t seem to ' import'

[Andy Balba]

if file hh.d  contains :
   int hh_t ( int x)
   { writeln ("hhh x= ", x );
   }

and file test.d (in same dir as file hh.d ) contains :

import std.stdio ;
import hh ;
void main()
{  hh_t(3);
}

Why does compiling test.d generate an "undefined ref"   ?