else:
    return res

```

Besides defining new ops, composition can be specified for an existing op
for portability. The following code defines the semantics of `AddNOp`:

```python
@Composite('AddNOp')
def _my_op_c(ins):
  N = len(ins)
  if N == 1:
    return ins[0]
  sum = ins[0]
  for i in range(1, N):
    sum += ins[i]
  return sum
```