Marshall Pease: 2 puzzles worth knowing

2 puzzles from Marshall Pease, each explained in a minute and credited to the original work. Free on Savvy.

Can generals surrounding a city ever fully trust a message passed by hand?
Several army divisions, each led by a general, surround an enemy city and can only communicate by sending messengers. They must unanimously agree to attack together or retreat toge…
— Leslie Lamport, Robert Shostak and Marshall Pease, The Byzantine Generals Problem
Some of the generals are traitors, can the loyal ones still agree on a plan?
Several divisions of an army, each led by a general, surround an enemy city. They must all attack together or all retreat together to avoid disaster, communicating only by messenge…
— Leslie Lamport, Robert Shostak, and Marshall Pease, The Byzantine Generals Problem

Five ideas worth knowing, every week