Function column_batch_error 

pub fn column_batch_error(
    num_batches: usize,
    k: usize,
    field_bits: usize,
) -> ErrorBits

Error of batching num_batches column openings with k fresh coordinates each.

Every coordinate is sampled independently from the transcript after the claimed column values are bound. A nonzero discrepancy therefore survives with probability at most num_batches * k / |F|.