The three camera angles of the “Vitameatavegamin” episode of I Love Lucy on the Monster, 1952.
An essay about Dann Cahn, the principal editor of the I Love Lucy show, explains how he created a system to cut the three strips of film generated by the new multicam mode of production:
https://www.editorsguild.com/FromTheGuild.cfm?FromTheGuildid=119
Carrie Puchkoff, “I Love Lucy… and Dann Cahn, too,” Motion Picture Editors Guild, November 4, 2009.