obj L = l:L and a:A;
obj A = integer;
var l:L;

op O(l:L) = (
    l.a = 10;
    l.l.l.l.l.a = 10;
);

op O2(i:integer) = (
    O(1);	-- ERROR: the integer 1 is not compat with tuple of L and A
    O({nil,1});
    O({{nil,1},2});
    O({{{nil,1},2},3});
);