function search() {
    // the search system object
    var s = {};

    function jointitles(x) {
        var l = [];
        for (var i = 0; i < x.length; i++) {
            l.push({
                id: x[i],
                title: titles[x[i]] || ''
            });
        }
        return l;
    }

    function intersect(a, b) {
        var c = [];
        for (var i = 0; i < a.length; i++) {
            if (b.indexOf(a[i]) !== -1) {
                c.push(a[i]);
            }
        }
        return c;
    }

    function cleansplit(q) {
        var terms = q.split(/\s+/);
        if (!terms.length) return [];
        terms = terms.map(function(t) {
            var clean = t.replace(/[^A-Za-z]/g, '');
            if (!clean) return false;
            else return clean.toLowerCase();
        }).filter(function(t) {
            return t;
        });
        return terms;
    }

    function isEmpty(obj) {
        for (var key in obj) return false;
        return true;
    }

    function autocomplete(q, callback) {
        var terms = cleansplit(q);
        if (!terms) return [];
        var last = terms.pop(), limit = 20;
        var pos = trie;
        // inch up pos to end
        var prefix = '';
        for (var i = 0; i < last.length; i++) {
            if (pos[last[i]]) {
                prefix += last[i];
                pos = pos[last[i]];
            }
        }
        var strs = [];
        function traverse(pos, prefix) {
            if (strs.length > limit) return strs;
            if (isEmpty(pos)) {
                strs.push(prefix);
            }
            for (var i in pos) {
                traverse(pos[i], prefix + i);
            }
        }
        traverse(pos, prefix);
        return strs;
    }

    function query(q, callback) {
        var terms = cleansplit(q);
        var index = index_d;
        if (!terms) return callback([]);
        function doterm(idx) {
            var term = terms.pop();
            if (!index[term]) return callback([]);
            if (idx) {
                idx = intersect(idx, index[term]);
            } else {
                idx = index[term];
            }
            if (!idx) return callback([]);
            if (terms.length) {
                doterm(idx);
            } else {
                return callback(idx);
            }
        }
        doterm();
    }

    s.query = query;
    s.autocomplete = autocomplete;

    return s;
}