Question: Naming variables/formula's

Wis_BS2_Taak2_2019-2020_20200323-1.mw

Hello,

I have some huge troubble with making sure all formula's wont be forgotten by Maple.

For example:

f(x):=a+b;
a:=5;
b:=2;
f(x):=f(x);  --> gives me f(x):=f(x) instead of saying f(x):=7

In my document the naming is a bit more complex.

I have a variable named "M_Inwendig2[y]" in the uploaded document. When i name it "M_Inwendig2(y)" (notice [-->( )
maple refuses to use the previous filled/calculated variables.

Due to this error i have copy and pasted the answer to a new formula to continue my work, therefor it becomes quite messy... Now i am trying to fix this.

Ideal all names will be M[inwendig2](y). So the first letter will tell the kind of variable (Moment) the subscript will tell the part (inside) and the depending variable will be between ().

In the document i have marked all error's and copy's RED.

Anyone can advice me? i have named variables the same way in the past, but now it doesnt work.

Regards,