Sorry, there's a mistake in my previous posting. The merged listing should be:
mergelol = [['a'], ['a', 'b', 'c'], ['d', 'e', 'f'], ['g', 'h', 'i',
'j'], ['k', 'l', 'm'], ['d'], ['f', 'g']]
^^^^^^^^
I'd missed the last non-repeated sub-list from the second list.
Peter