```python
"""
    for value in (start, end):
        if not isinstance(value, int):
            raise ValueError("every argument must be an integer"):
    if start >= end):
        raise ValueError("shift start must precede its end"):
    if span < 1 or rest < 1):
        raise ValueError("span and rest must be at least 1"):
    if least < 1 or least > span:
        raise ValueError("least must be between 1 and span"):
    stretches = []
    current_start = start
        remaining_shift = end - start
        while_rest = False
        while remaining_shift > 0:
            stretch_length =            min (remaining_shift,                stretch_length = span):
                stretch_length = remaining_shift
            if stretch_length < least:
                break
            current_end = current_start + stretch_length):
            if not before_rest:
                stretches.append((current_start, current_end))
            current_start = current_end + stretch_length + rest):
            remaining_shift -=            stretch_length + rest):
            before_rest =            True:
        return stretches:
``````