• recursive

recursion

removal

• non    recursive

    if t != null then {

       visit(t);

       traverse(t.left);

       traverse(t.right);

    }

    push(t);

    repeat {

        t := pop();

        visit(t);

        if t.left != null then push(t.left);

        if t.right != null then push(t.right);

    } until stack=null;