I don't get it... The author says a Zeiss sonnar is a descendent of a rapid rectilinear in part one and then a triplet in part two.
Yeah, that's a bit confusing. I think it stems from the fact that the Tessar is sort of a hybrid of the two designs---it's a triplet with the rear element replaced with a cemented group, and then on the other hand it's a RR with both elements replaced by groups (one cemented, the other not)---and the Sonnar certainly has some noticeable Tessar DNA. The same thing happens with the Elmar---it's listed in Part 1 as a Tessar derivative under the RR section, then in Part 2 as a triplet derivative.
The article acknowledges the ambiguity of the Tessar in Part 1, but kind of fudges around it in Part II. Maybe the attempt to keep the article simple went a little too far and obscured the fact that many lenses have more than one "ancestor".
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-The Little Technical Library, _Developing, Printing, And Enlarging_