docs: function(df) {
           return {
              d: function(x, logp) { return dt(df, logp)(x); },
              p: function(q, lowerTail, logp) {
                 return pt(df, lowerTail, logp)(q);
              },
              q: function(p, lowerTail, logp) {
                 return qt(df, lowerTail, logp)(p);
              },
              r: function() { return rt(df)(); }
           };
        }