function get_double_key:integer;
 var time,key:integer;
begin
 key:=getkeyclicked;
 if key<>0 then begin
 time:=getrelativetimems;
 if (getkeyclicked=key) and (getrelativetimems-time<500) then begin
 get_double_key:=key; end;
 else
 get_double_key:=0;
 end;
end;