Dane's Texter

Function only works with keyword arguments. Something like arkalii's solution is a good way of dealing with the issue. You could also use a decorator on the add function to map argument names. This would keep the mappings clean:
arg_map = {
    "num1": "x",
    "n":    "x",
    "num2": "y",
    "m":    "y",
}

def replace_args(func):
    def new_func(*_, **kwargs):
        # Generate a new kwargs dictionary with replaced keys.
        new_kwargs = {}
        for k, v in kwargs.items():
            if k in arg_map:
                new_kwargs[arg_map[k]] = kwargs[k]

        return func(**new_kwargs)

    return new_func

@replace_args
def add(x, y):
    return x + y

@replace_args
def minus(x, y):
    return x - y