Andys code:

22.times |Int c|
{
  users.add(User { it.id=c; })
  cols.add(map[users[c]])
}

....

11.times |Int c|
{
  11.times |Int z|
  {
    if (c == z) return
    verifyNotEq(cols[c], cols[z])
  }
}

UserColorMapTest.fan(13,3): Internal error: duplicate slot c$0

I've seen it in another case too.

Promoted to ticket #528 and assigned to brian

Ticket resolved in 1.0.42