mordicai has known Katja since she was a wee sprout growing in a nutshell.  She lived in Sweden & they communicated via electrostatical telegraphy, until someone got off their keister and invented the telephone already, which made things much easier.  Eventually they stopped talking to each other, but Olive fixed that when she came to Babylon to visit...it turned out that Katja had moved there earlier that year!  Since then they've been a puddle of do-nothing together.