I keep coming back to Peirce’s early lectures on the logic of science because we see there the first inklings of his prospective theory of information, one of those ideas whose time was ripe enough but whose complete fruition lies yet in the future. The ideas of constraint, definition, determination, information, and inquiry are naturally deeply intertwined.
Here is a link to my ongoing study of those lectures, focusing on the formula:
Definitions of Peirce’s various terms (content, sphere, etc.) may be found there.