class Interval {
    has Real $.lb = die 'Lower bound is required';
    has Real $.ub = die 'Upper bound is required';

    method update(:$lb = $.lb, :$ub = $.ub) {
        die "Require lb <= ub" unless $lb <= $ub;
        ($!lb, $!ub) = ($lb, $ub);
    }
}