<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def iflatten(seq, isSeq=isSeq):
 r"""Like `flatten` but lazy."""

    for elt in seq:
        if isSeq(elt):
            for x in iflatten(elt, isSeq):
                yield x
        else:
            yield elt