merge xs@(x : xs') ys@(y : ys') = if x <= y then x : merge xs' ys else y : merge xs ys'
merge xs@(x : xs') ys@(y : ys') = if x <= y then x : merge xs' ys else y : merge xs ys'
merge xs@(x : xs') ys@(y : ys') = if x <= y then x : merge xs' ys else y : merge xs ys'