I was trying to follow the example provided by [this blog post](https://mattsenior.com/2014/02/using-clojures-core-logic-to-solve-simple-number-puzzles) and found that it only worked if I removed the conditions that test for subtraction with a negative result. I removed a lot of different things and found that even this basic example does not find any matches:

```
(ns example.core
(:refer-clojure :exclude [==])
(:require [clojure.core.logic :refer :all])
(:require [clojure.core.logic.fd :as fd]))

(run* [q]
(fresh [a0 a1]
(== q [a0 a1])
(fd/in a0 a1 (fd/interval 1 9))
(fd/- a0 a1 -1)
;(fd/eq
; (= (- a0 a1) -1))
))
```

Dependencies (though I tried clojure 1.8 and 1.9 too):
```
:dependencies [[org.clojure/clojure "1.7.0"]
[org.clojure/core.logic "0.8.11"]]
```