Function checked_fold 

fn checked_fold(
    table: &Table,
    model: &FastText,
    ids: &[usize],
    words: &[Vec<String>],
    messages: &[Message],
) -> Result<f64, LearnError>

The largest difference between the table’s probability, Platt aside, and fastText’s own prediction, on messages ids (500 at most); over 1e-4, the fold is broken and nothing is exported.