#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
Substraction operation.
"""


def minus_one(a):
    """Return a - 1.
    """
    return a - 1


def minus_two(a):
    """Return a - 2.
    """
    return a - 2


def minus_three(a):
    """Return a - 3.
    """
    return a - 3


def minus_four(a):
    """Return a - 4.
    """
    return a - 4
