# `≡` — Depth / Match

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

`≡Y` gives nesting depth: 0 for an atom, and otherwise 1 more than the
deepest item. An empty array takes the depth of its prototype.

``` bpl
≡1 2 3             ⍝ 1ₓ
≡[1 [2 3]]         ⍝ 2ₓ
≡5                 ⍝ 0ₓ
```

`X≡Y` tests equal shape and corresponding contents, using tolerant
numeric equality. NaN matches NaN. The result is one Boolean.
[`=`](equals.qmd) compares item by item instead.

``` bpl
1 2≡1 2            ⍝ $t
1≡,1               ⍝ $f
```