 Starting in 1916, and culminating in his 1929 "Process and Reality", A. N. Whitehead published several books invoking part–whole concepts of varying degrees of formality; see Whitehead's point-free geometry.Part–whole theory has been superseded by a collection of fully formal theories called mereology, Stanislaw Lesniewski's term for a formal part–whole theory he began expositing in 1912.Over the course of the 20th century, a number of Polish logicians and mathematicians contributed to this "Polish mereology."