Function lemma_u16_clearbit_bit_unchanged 

pub broadcast proof fn lemma_u16_clearbit_bit_unchanged(word: u16, b: int, b2: int)

requires

0 <= b < 16,

0 <= b2 < 16,

b != b2,

ensures

u16_bit_is_set(word & (!(1u16 << (b as usize))), b2) == u16_bit_is_set(word, b2),

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