I have the following function
$$ f(a,b,c\mid k) = \binom{k}{l}a^l\binom{k-l}{m}b^mc^{k-l-m}[1-d^m] $$ Upon application of the binomial theorem I get
$$ [a+b+c]-[a+bd+c] $$ I do not wish to simplify this further.
I would also like to consider $f^2$. It is at this point I am unsure how to proceed, starting from my original expression. How would I rationalise this?