Digilogic

The expression I am dealing with is

a += ---b--;

That is just a small portion of the statement but my job is to add parenthesis to enforce the implicit c precedence rules.

I haven't been able to come up with a way to make this work.
I keep getting the compile error invalid lvalue in decrement when I try things such as:
a = -(--(b--));
a = -((--b)--);
etc...

Any ideas why this won't run?

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