This is a simple reference request, for the origin of a particular type of paradoxical statement. The example I remember is
Roger Penrose can't consistently claim this statement to be true.
It's a true statement, but if you happen to be Roger Penrose you can't say so without contradicting yourself. I have a feeling it might be due to (or popularised by) Douglas Hofstadter, but I'm not sure.
Note: it's a different statement from
Roger Penrose can't consistently believe this statement to be true.
It would be helpful to know the origin of both statements, but I'm particularly interested in the first, in which the target person can know the statement to be true but can't consistently say so.