Let's go back now to the simpler version of the problem, where we replace in case-sensitive way. Our original version of the code applies the replacement only once. That is, if the dictionary d maps:

d = {"cats": "dogs", "dogs": "pigs"}

and our text is t = "I love cats", the function replace_once(t, d) applies the replacement only once, and we obtain

"I love dogs"

Now, you should write a function replace_chain, that keeps applying replacements until no more replacements can be applied, so that replace_chain(t, d) yields:

"I love pigs"

def replace_chain(t, d):

"""

@param t: a string

@param d: a dictionary, mapping words to their replacements

@returns: a string, where words in d have been replaced according to the dictionary mapping,

repeating the replacements until no replacement can be applied.

"""

# YOUR CODE HERE

raise NotImplementedError()