Function lemma_u8_clearbit_bit_unchanged 

pub broadcast proof fn lemma_u8_clearbit_bit_unchanged(word: u8, b: int, b2: int)

requires

0 <= b < 8,

0 <= b2 < 8,

b != b2,

ensures

u8_bit_is_set(word & (!(1u8 << (b as usize))), b2) == u8_bit_is_set(word, b2),

Clearing bit b leaves a different in-range bit b2 unchanged.