Wonder

Maybe this is an attempt at a question about scope.

(1) That first order logic is undecidable

and

(2) Not that first order logic is undecidable

both seem to have the proposition that first order logic is undecidable as bits. Is negation included in the second proposition?

(1) That first order logic is undecidable

and

(3) That first order logic is not undecidable

seem to have different proposition, since negation seems clearly to be a part of the proposition's make up.

Is it plausible to say that (1) and (2) contain the same proposition, but that (2) says of the same proposition as in (1) that it is false? It seems so to me, and that the proposition in (3) is not the proposition in (1) or (2).