The first three operations reduce the number of terms in the expansion and thus strictly simplify the expression (in terms of how many terms there are), but the last may need to be used several times before it "simplifies" the expression (for example, in terms of how many repeated terms there are). Nonetheless, this simplification procedure terminates, as it is impossible to get stuck in an infinite loop using the last operation alone. (Proof: we may assume that the $n_i$ are positive. Then all of the operations either reduce the number of terms, or the sum of the $n_i$.)
Is the proof above correct? (If not, and the original claim is correct, can you give me a representation of the number 5473?)
Assuming the proof is correct, is the original claim true for other non-integer bases? What I mean is the following: