Usage
# S4 method for brob
[(x, i, j, ..., drop = TRUE)
# S4 method for glub
[(x, i, j, ..., drop = TRUE)
# S4 method for brobmat
[(x, i, j, ..., drop = TRUE)
# S4 method for brob
[(x, i, j, ...) <- value
# S4 method for glub
[(x, i, j, ...) <- value
# S4 method for brobmat
[(x, i, j, ...) <- value