More likely a hat (following Russel's Principia) maybe simulated as a `/\` capital Greek letter "L" which then was changed to the Greek lower letter lambda. Chu

More likely a hat (following Russel's Principia) maybe simulated as a `/\` capital Greek letter "L" which then was changed to the Greek lower letter lambda. Church's book in 1941 was typed using what looks like a typewriter. The name was catchy though.