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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 _allowed(to_op, from_op, rhs):
    "Determine if a mutation from `from_op` to `to_op` is allowed given a particular `rhs` node."
    if is_none(rhs):
        return to_op in _RHS_IS_NONE_OPS.get(from_op, ())

    if is_number(rhs):
        return to_op in _RHS_IS_INTEGER_OPS

    return True