Ross had a correspondence with the French mathematician Jacques Riguet between 1953 and 1959. Unfortunately, we do not have Riguet's replies, however, it is clear that Riguet's work resonated with Ross's own approach so well that Ross suggested they consider writing a book together on the theory of biological relations.
Although there is no first-level index card for Riguet in Ross's alphabetical index, Ross mentioned Riguet many times in his Journal's summaries and second-level index entries. Those Journal entries are included below, interleaved chronologically with the letters to help show how Ross was influenced by Riguet.
Confluantgeneralisation of step-function Step function what matters is the confluent Oddments : Carry out the program of pages 6184 (foot) and 6185 (top). Summary: I should re-read my Notes, Vol. 5 or so onwards, reading "lots of step-functions" as the more general "lots of equilibria",
and lots of step-surfaces" as "lots of boundaries of confluents".