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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_valid_identifier(identifier):
 """Checks if the given identifier is valid or not. A valid identifier may consists of the following characters with a maximum length of 100 characters, minimum of 1 character. Valid characters for an identifier, - A to Z - a to z - 0 to 9 - _ (underscore) - - (hypen) """

    if not isinstance(identifier, basestring):
        return False

    if len(identifier) > 100 or len(identifier) < 1:
        return False

    condensed_form = set(list(identifier.lower()))
    return condensed_form.issubset(VALID_IDENTIFIER_SET)