lengthnil0lengthconsxlslengthlltx0falselt0sytrueltsxsyltxyheadconsxlxheadnilundefinedtailnilniltailconsxllreverselrev0lnillrevxlaccuorigifltxlengthorigxlaccuorigiftruexlaccuorigrevsxtaillconsheadlaccuorigiffalsexlaccuorigaccu2.0lengthconsxllengthlltsxsyltxyreverselrev0lnillrevxlaccuoriglengthorigrevxlaccuorigltxlengthorigrevxlaccuorigifltxlengthorigxlaccuorigiftruexlaccuorigheadliftruexlaccuorigtailliftruexlaccuorigrevsxtaillconsheadlaccuorigtruereverselrev0lnillfalseiftruexlaccuorigrevsxtaillconsheadlaccuorigrevxlaccuorigifltxlengthorigxlaccuorigtrueiftruexlaccuorigtaillfalseiftruexlaccuorigheadlfalserevxlaccuorigltxlengthorigfalseltsxsyltxytruelt22revxlaccuoriglengthorigfalselengthconsxllengthltruelength11