Get the "right" subset of the nonempty set.
For empty sets, returns
From a user perspective, this should likely be viewed as an arbitrary proper subset excluding the head and disjoint from the left subset. Concretely, it is the subset for which the head is bst< all elements. In terms of the underlying tree representation, this is the right subtree.
Function:
(defun right$inline (set) (declare (xargs :guard (setp set))) (tree-right (sfix set)))
Theorem:
(defthm setp-of-right (b* ((right (right$inline set))) (setp right)) :rule-classes :rewrite)