import re


def tokenize_en(text):
    """A basic English tokenizer which splits and does basic filtering.
    The included filters and transformations include:
    * lower case each token
    * filter out non-alphabetic characters for English
    """
    tokens = text.split()
    lowercase_tokens = [token.lower() for token in tokens]
    filtered_tokens = [re.sub(r'[^a-z]', '', token) for token in lowercase_tokens]
    english_tokens = [token for token in filtered_tokens if token != '']
    return english_tokens