You are seeing a 41-year-old male in a GP setting who has presented with a tongue lesion. On examination you note that there is a white patch adhering to the right-side of the tongue. You note that the patch is bright white and sharply defined with the surfaces of the patches appearing slightly raised above the surrounding mucosa. The patient informs you that he has tried to rub this patch off but he has had no success. All observations are within normal limits and your patient is systemically well. What is the most likely diagnosis?