In philosophy, specifically metaphysics, mereology is the study of parthood relationships. In mathematics and formal logic, wellfoundedness prohibits ⋯ < x < ⋯ < x < ⋯ {\displaystyle \cdots <x<\cdots <x<\cdots } for any x. Thus non-wellfounded mereology treats topologically circular, cyclical, repetitive, or other eventual self-containment. More formally, non-wellfounded partial orders may exhibit ⋯ < x < ⋯ < x < ⋯ {\displaystyle \cdots <x<\cdots <x<\cdots } for some x whereas well-founded orders prohibit that.
See also Aczel's anti-foundation axiom Peter Aczel John Barwise Steve Awodey Dana Scott
External links "Non-wellfounded Set Theory" entry by Lawrence S. Moss in the Stanford Encyclopedia of Philosophy, 2017-01-05
