# `≠` — Unique mask / Not equal

Function. Keys: `Alt-Shift-=`. Ranks: `∞` monadic, `0 0` dyadic

`≠Y` marks the first occurrence of each distinct major cell.
[Tolerance](../evaluation.qmd#equality-and-ordering) decides which cells
are distinct.

``` bpl
≠3 1 3 2 1         ⍝ $t $t $f $t $f
```

`X≠Y` tests inequality, pervasively.

``` bpl
1 2 3≠2            ⍝ $t $f $t
```

## Inverse

On Booleans, `≠` is its own inverse with either argument fixed.

``` bpl
1 0≠⁻¹1 1   ⍝ $f $t
```