Question: A problem for "Error, invalid 'if' statement"


I use some codes to find the coefficients of given functional expressions. But in the procedure of operation, "Error, invalid 'if' statement" is showed. How can I do to solve the error?
If this structure of code can't find the coefficients, how to get the coefficients?

P.S. the coefficients of given functional expressions like this:

given Ex:=a*x+b*y-d*z+e*y-f*x-m*z,

given functional expressions are   Base:={x,y,z}.

the coefficient of x is a-f;

the coefficient of y is b+e;

the coefficient of z is -d-m.

In file 'Download', the Ex and Base are complicated.

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