while trying to help a user who was facing an unhelpful
```
omega did not find a contradiction:
[0, 0, 0, 0, 1, -1] ∈ [1, ∞)
[0, 0, 0, 0, 0, 1] ∈ [0, ∞)
[0, 0, 0, 0, 1] ∈ [0, ∞)
[1, -1] ∈ [1, ∞)
[0, 0, 0, 1] ∈ [0, ∞)
[0, 1] ∈ [0, ∞)
[1] ∈ [0, ∞)
[0, 0, 0, 1, 1] ∈ [-1, ∞)
```
I couldn’t resist and wrote a pretty-printer for these problem that
shows the linear combination as such, and includes the recognized atoms.
This is especially useful since oftem `omega` failures stem from failure
to recognize atoms as equal. In this case, we now get:
```
omega-failure.lean:19:2-19:7: error: omega could not prove the goal:
a possible counterexample may satisfy the constraints
d - e ≥ 1
e ≥ 0
d ≥ 0
a - b ≥ 1
c ≥ 0
b ≥ 0
a ≥ 0
c + d ≥ -1
where
a := ↑(sizeOf xs)
b := ↑(sizeOf x)
c := ↑(sizeOf x.fst)
d := ↑(sizeOf x.snd)
e := ↑(sizeOf xs)
```
and this might help the user make progress (e.g. by using `case x`
first, and investingating why `sizeOf xs` shows up twice)
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