Given these definitions:

```
zipPlus [] _ = []
zipPlus _ [] = []
zipPlus (x:xs) (y:ys) = x+y : zipPlus xs ys

ts = 1 : zipPlus ts ts
```

(a) [2 marks] Calculate the successive approximations of ts, up to and including
ts4.  Show some steps.  You can write ⊥ or _|_ for the bottom/undefined symbol.

ts0 = ⊥

ts1 =

ts2 =

ts3 =

ts4 =


(b) [1 mark] Make a guess and describe what infinite list ts is.