Very nice, thanks for sharing! Maybe show which upper or lower values are included in the intervals? A notation I am familiar with uses outward facing brackets if the value is not included in the interval. That always applies to infinity.

Applied to the cases here:

]-∞, -1] U [0.5, +∞[

The excluded interval in between becomes ]-1, 0.5[ then.

That’s how min (and analogously max) works, right? min(A, B) = [lo(A,B), lo (hi(A), hi(B))].

Edit: idea: copy a formula from the results section to the input field if the user clicks/taps on it.