Compute the union of intervals in one or more interval matrices. The
  intervals contained in a single interval matrix object need not, in
  general, be disjoint; interval_union, however, always returns a
  matrix with sorted, disjoint intervals.
# S4 method for Intervals_virtual
interval_union(x, ..., check_valid = TRUE)# S4 method for missing
interval_union(x, ..., check_valid = TRUE)
A single object of appropriate class, compactly representing the union
  of all intervals in x, and optionally, in ... as
  well. For class "Intervals", the result will have the same
closed values as x.
An "Intervals" or "Intervals_full" object.
Optionally, additional objects which can be combined with
    x. See c.Intervals for details on mixing
    different types of objects.
Should validObject be called before passing to
    compiled code? Also see interval_overlap.
All supplied objects are combined using c
  and then then passed to reduce. The missing
  method is only to permit use of do.call with named list,
  since no named element will typically match x.
See reduce, which is used to produce the results.