Module algebra 

The Kleene / De Morgan lattice on the likeliness scale. These are the logical connectives of the calculus; the non-probabilistic character lives here (no excluded middle, no contradiction collapse).

Functions

and

Conjunction — the meet (weakest link): a claim resting on both a and b is no more expected than its least-expected part.

combine_premises

Likeliness of a conjunction of premises = the weakest (meet over all). The vacuous conjunction (no premises) is Certain (the top).

combine_routes

Likeliness of a conclusion reachable by alternative routes = the strongest (join over all). The vacuous disjunction (no routes) is Impossible (the bottom).

not

Negation — the order-reversing involution Impossible ↔ Certain, Even fixed. Note not(not(l)) == l, but or(l, not l) need not be Certain.

or

Disjunction — the join (best alternative): a claim reachable via a or b is at least as expected as its most-expected route.