well, if you take away the last 2 element ( its field flattener quite obviously ) and look at the diagram, now picture the first 3 element as cemented together, you can see that this is pretty much Sonnat design( sort of ) ..
I say sort of because one of the character of Sonnar design is that cemented part ( strong interface ) but now the 3 element cemeted front group is splitted totally into air spaced and this is more like conventional corrective surface, The rear group with the extra element at the back is pretty much classic Sonnar though ... Or it might be just hybrid design taking the old Biotar backend ( pre-war Biotar ). Without any knowledge of the glass , its difficult to tell.
IMHO , at this wide coverage they can choose to use the Biogon but since Biogon design ( whether it be pre war or post war ) is pretty much almost impossible to be made at such speed. The Optical designer just use the same triplet derived Sonnar and inject some of the Biogon design into it to made that wide enough but allow for the speed. ( Just my 2 cents )
These days with computerized CAD and design / simulation its easy to mix and match optical groups to form lens. Well for onec at least Zeiss and Leica is not cheating as Olympus do. After reading the
Photozone review on the recent so hyped up 12mm/2.0I am just about dash all my expectation with Olympus on M4/3