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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 link_docstring(modules, docstring:str, overwrite:bool=False)->str:
    "Search `docstring` for backticks and attempt to link those functions to respective documentation."
    mods = listify(modules)
    for mod in mods: _modvars.update(mod.__dict__) # concat all module definitions
    return re.sub(BT_REGEX, replace_link, docstring)