message: dr::replace_grad: fix typo
diff: @@ -2305,7 +2305,7 @@ def replace_grad(a, b):
  elif lb == 1 and depth == 1:
  b = b + zero(tb, la)
  else:
  - raise Exeption("replace_grad(): input arguments have "
  + raise Exception("replace_grad(): input arguments have "
  "incompatible sizes (%i vs %i)!"
  % (la, lb))
  