| ⊦ bits.first ∧ # bits = # bits1 + 1 ∧ bits1 ≠ [] ∧ bits0 ≠ [] → bitsand(bits, bits0 + bits1) = bits0 + bitsand(bits.rest, bits1) |
# bits = # bits1 + 1, bits.first ⊦ bits1 = [], bits0 = [], bitsand(bits, bits0 + bits1) = bits0 + bitsand(bits.rest, bits1)