original.name="UnionType_Valid_28"
whiley.compile.ignore=true
WhileyCompiler.issue=1095
======
>>> main.whiley
type Tree is null | Node

type Node is { int data, Tree left, Tree right }
// Data in nodes reachable from left must be below this
where left is Node ==> left.data < data
// Data in nodes reachable from right must be above this
where right is Node ==> right.data > data

public export method test():
    Node n1 = { data: 1, left: null, right: null }
    Node n2 = { data: 2, left: n1, right: null }
    Node n3 = { data: 0, left: null, right: n1 }
    //
    assert n2.left == n1
    assert n2.right == null
    assert n3.left == null
    assert n3.right == n1
---