program test3;
function a(m,n:integer):integer;
var x:integer;
begin
if m=0 then x:=n+1
else if n=0 then x:=a(m-1,1)
else x:=a(m-1,a(m,n-1));
a:=x;
end;
begin{main}
writeln(a(1,2));
end.
输出：4