Question 12.1.2: Write a procedure that checks if an element t : Tis present......

..t is not in the tree

end else begin

x := root ;
{invariant:  it remains to check if t is present in
a nonempty subtree rooted at x}
while  ((t < val [x]) and (left  [x] <> null)) or
((t > val [x]) and (right  [x] <> null)) do begin

if t < val [x] then begin {left  [x] <> null}

I x := left [x];

end else begin {t > val [x], right  [x] <> null}

x := right  [x];

end;

end;
{either t = val [x] or t is not in the tree}
..answer is (t = val [x])

end;