Seinfeld to Sierra

Mad About You's Paul leased his old apartment to Seinfeld's Kramer.

Mad About You's Paul did a documentary narrated by The Dick Van Dyke Show's Alan Brady.

Sally Rogers from The Dick Van Dyke Show was on Hi Honey, I'm Home!

Alice & Trixie from The Honeymooners crossed over onto Hi Honey, I'm Home!

Here's Lucy's Lucy was driven around Miami by Ralph Cramden of The Hooneymooner's

Here's Lucy's Lucy Carter and Mannix's Mannix are held hostage in an episode of Here's Lucy.

Mannix returned to TV on an episode of Diagnosis Murder to solve an old unsolved case with the help of Dr Mark Sloan.

Diagnosis Murder's Dr Mark Sloan was defended by Matlock when Sloan was accused of murder

Both feature the fictional Trans Global Airlines

The fictional Sierra National Park of Sierra is in the same universe as Emergency!