≡ — 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.

≡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. = compares item by item instead.

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