Tensor.swap_perm: def of bendtorch@1.3.0.0
Import: import bendtorch@1.3.0.0/tensor.bend as Tensor
Lines 518-524 of bendtorch@1.3.0.0/tensor.bend: https://jend.leeeet.dev/read.txt?path=bendtorch@1.3.0.0/tensor.bend&start_line=518&end_line=524

import Base

# 0..n-1 with i and j swapped
def swap_perm(n: Nat, +i: Nat, +a: Nat, +b: Nat) -> List<&2, Nat>:
  match n:
    case 0n:
      Nil{}
    case 1n+r:
      Bool.pick(Nat, Nat.is_eq(i, a), b, Bool.pick(Nat, Nat.is_eq(i, b), a, i)) <> swap_perm(r, 1n+i, a, b)

Uses (4):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool.pick
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.is_eq