if isCleanExt(v) && ft.isNonNegative(v.Args[0]) {
		return true
	}

	// Check if the signed poset can prove that the value is >= 0
	return ft.orderS.OrderedOrEqual(ft.zero, v)
}

// checkpoint saves the current state of known relations.
// Called when descending on a branch.
func (ft *factsTable) checkpoint() {
	if ft.unsat {
		ft.unsatDepth++
	}