Function lemma_u128_clearbit_not_bit_is_set 

pub broadcast proof fn lemma_u128_clearbit_not_bit_is_set(word: u128, b: int)

requires

0 <= b < 128,

ensures

!u128_bit_is_set(word & (!(1u128 << (b as usize))), b),

Clearing bit b makes that bit clear.