Tensor.at1: def of bendtorch@1.3.0.0
Import: import bendtorch@1.3.0.0/tensor.bend as Tensor
Lines 32-40 of bendtorch@1.3.0.0/tensor.bend: https://jend.leeeet.dev/read.txt?path=bendtorch@1.3.0.0/tensor.bend&start_line=32&end_line=40

import Base

# size of axis k (1 past the last axis, so a missing axis counts as a size-1 one)
def at1(s: List<&2, Nat>, k: Nat) -> Nat:
  match s k:
    case Nil{} _:
      1n
    case Con{h, t} 0n:
      h
    case Con{h, t} 1n+p:
      at1(t, p)

Uses (2):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat