Quick question: in the proposed rewording of intro.execution¶8, why is the following rewriting “((a + b) + 32765)” not reintegrated at the end of the untouched

Quick question: in the proposed rewording of intro.execution¶8, why is the following rewriting “((a + b) + 32765)” not reintegrated at the end of the untouched text? Have I misunderstood that with two's complement this would be legal?