Provenance displays incorrect facts in derivation tree for less-than relation

[justinlubin]

Steps to reproduce

1. Create a file test.dl with the following content:

.decl node(x: number)

.decl link(x: number, y: number, z: number)
.output link

node(1).
node(2).
node(3).

link(x, y, z) :- node(x), node(y), node(z), x < y, y < z.

2. Run souffle -texplain test.dl and enter the command explain link(1, 2, 3).

Expected output

node(1) node(2) node(3) 1 < 2 2 < 3
--------------------------------(R1)
           link(1, 2, 3)

Actual output

node(1) node(2) node(3) 1 < 2 1 < 1
--------------------------------(R1)
           link(1, 2, 3)

This derivation tree is incorrect because the premises in the top-right corner do not match up with the premises in the definition of link; moreover, the 1 < 1 premise is simply not true.

P.S. Thanks for all your work on Soufflé — the tool and papers are amazing! :)