Question: Sum every fifth term in an expression

Hi... I have a long-expression, which I have abbreviated here. I want every 5th term summed. Included is my code, but I need the unassign command (after point 12) for it to work. The problem is when I unhash and insert this unassign('s','X[4]') command into my actual Table of Records procedure, Maple protests. it gives a cryptic: " Error, `(` unexpected " .
How can I modify the original code to sum every 5th term as efficiently as possible as the thing is a 4000 term expression which I later need to numerically integrate?


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