Investigate the use of e-graph/equality saturation

[brandonwillard]

Per some external conversations, it might be worth looking into a means of encoding and enumerating stream disjunctions in a global e-graph-like miniKanren state and using those as part of the complete search process.

Basically, an e-graph-like structure would serve as a "global" component of a miniKanren state and consist of logic variable mappings that—unlike standard state objects—would map variables to multiple unification results, such as those arising from conde disjunctions.