How to complete the proof of the theorem about associative property?

90 Views Asked by At

Let $A$ be set of numbers. Prove that if * operation is associative for any $3$ elements from $A$, the operation is associative for any $n$ elements from $A$, too.
Intuitively, this can be proved by the method of Mathematical Induction, but I don't know how to go further after inductive step.