Methods for dealing with sparse geometry binary predicate lists
Details
sgbp are sparse matrices, stored as a list with integer vectors holding the ordered TRUE indices of each row. This means that for a dense, \(m \times n\) matrix Q and a list L, if Q[i,j] is TRUE then \(j\) is an element of L[[i]]. Reversed: when \(k\) is the value of L[[i]][j], then Q[i,k] is TRUE.
== compares only the dimension and index values, not the attributes of two sgbp object; use identical to check for equality of everything.
