Chapter 6.1, Problem 8E

(a)

To determine

To prove:

  $\left(a_1\ast a_2\right)\ast \left(a_3\ast a_4\right)=a_1\ast \left(\left(a_2\ast a_3\right)\ast a_4\right)$

(b)

To determine

To prove:

Any product of $n$ factors in that order is equal to the left associated product

  $\left(\mathrm{...}\left(\left(a_1\ast a_2\right)\ast a_3\right)\mathrm{...}\right)\ast a_n$