# Python: Negation

Along with the logical operators AND and OR, there is also an operation called “negation” It changes the logical meaning to the opposite. In programming, negation corresponds to the unary operator `not`:

``````not True   # False
not False  # True
``````

For example, if there's a function that checks if a number is even, then you can use negation to check if a number is odd:

``````def is_even(number):
return number % 2 == 0

print(is_even(10))      # => True
print(not is_even(10))  # => False
``````

In the example above, we added `not` to the left of the function call and got the opposite action.

Negation is a tool with which you can express intended rules in code without writing new functions.

If you write `not is_even(10)`, the code will still work:

``````print(not not is_even(10))  # => True
``````

In logic, double negation means positive:

``````not not True   # True
not not False  # False

print(not not is_even(10))  # => True
print(not not is_even(11))  # => False
``````

Now you know what the operators AND, OR and `not` mean. They allow you to specify compound conditions with two or more logical expressions.

## Instructions

1. Implement a function called `is_palindrome()` that determines whether a word is a palindrome or not. A palindrome is a word that reads the same way in both directions. Words may be passed to the function in any case, so you must first convert the word to lowercase: `word.lower()`.

``````is_palindrome('hut') # true
is_palindrome('hexlet') # false
is_palindrome('Argument') # true
is_palindrome('Function') # false
``````
2. Implement a function called `is_not_palindrome()` which checks if a word is NOT a palindrome:

``````is_not_palindrome('шалаш') # false
is_not_palindrome('Ага') # false
is_not_palindrome('хекслет') # true
``````

To do this, call `is_palindrome()` inside `is_not_palindrome()` and apply negation.

The exercise doesn't pass checking. What to do? 😶

• Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

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My code is different from the teacher's one 🤔

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