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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_discover(n):
 """Checks if credit card number fits the discover card format."""

    n, length = str(n), len(str(n))

    if length == 16:
        if n[0] == '6':
            if ''.join(n[1:4]) == '011' or n[1] == '5':
                return True
            elif n[1] == '4' and n[2] in strings_between(4, 10):
                return True
            elif ''.join(n[1:6]) in strings_between(22126, 22926):
                return True
    return False