Function lemma_u128_setbit_bit_unchanged 

pub broadcast proof fn lemma_u128_setbit_bit_unchanged(word: u128, b: int, b2: int)

requires

0 <= b < 128,

0 <= b2 < 128,

b != b2,

ensures

u128_bit_is_set(word | (1u128 << (b as usize)), b2) == u128_bit_is_set(word, b2),

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