Past exam of the year 1 of the computer science course of the University of Oxford / 2018 / Functional programming, design and analysis of algorithms / 2 / e

Addition and subtraction of formal power series are coefficientwise:

plus, minus :: Num a => [a] -> [a] -> [a]
plus  = zipWith (+)
minus = zipWith (-)

Here every valid input is an infinite coefficient list. If finite polynomial coefficient lists were admitted, they would need zero-padding before these definitions: ordinary list zip otherwise truncates to the shorter length.