     uIvl.union(ivl).equals(ivl).should.be.true
 
     ivl = new Interval(-100, 0)
-    (ivl.union(uIvl) == null).should.be.true
-    (uIvl.union(ivl) == null).should.be.true
+    should(ivl.union(uIvl)).be.null
+    should(uIvl.union(ivl)).be.null
 
     ivl = new Interval(8, 17)
     i = ivl.union(uIvl)


    x = new Interval(a,  d )
    y = new Interval(  b, e)
    (x.except(y).low  == a).should.be.true
    (x.except(y).high == b).should.be.true
    (y.except(x).low  == d).should.be.true
    (y.except(x).high == e).should.be.true

    x = new Interval(a,b,   )
    y = new Interval(    d,e)


    x = new Interval(a  ,  e)
    y = new Interval(  b,d  )
    x.intersect(y).should.eql y
    y.intersect(x).should.eql y

    x = new Interval(a,  d )
    y = new Interval(  b, e)
    x.intersect(y).should.eql new Interval(b, d)
    y.intersect(x).should.eql new Interval(b, d)

    x = new Interval(a,b,   )
    y = new Interval(    d,e)
