[poisondeathray]

If you double rate deinterlace it to 59.94, then step through frame by frame , look at the pattern during a scene with motion (such as a camera pan)

1) If there is motion every frame, then it's interlaced content (and you would want to use 59.94p when deinterlacing)
2) If you get duplicates , then it's 29.97p content (then should not deinterlace - you want to field match to 29.97p)
3) If you get 3:2 pattern of repeats, then it's 23.976p content (then you should not deinterlace - it needs to be IVTC'ed)

There are exceptions, and weird cadences, changing patterns, but those 3 should cover the majority of common scenarios