84 Conclusion of proof: associativity

(iv) This can be proved in a similar way to (i). Alternatively, one use (iii) to compute

$$ℒ((f\ast g)\ast h)(s)=ℒ(f\ast g)(s)ℒ(h)(s)=ℒ(f)(s)ℒ(g)(s)ℒ(h)(s)$$

$$=ℒ(f\ast (g\ast h))(s)$$

and then use uniqueness, as discussed below.