docs: function(mu, sigma) {
           return {
              d: function(x, logp) { return dnorm(mu, sigma, logp)(x); },
              p: function(q, lowerTail, logp) {
                 return pnorm(mu, sigma, lowerTail, logp)(q);
              },
              q: function(p, lowerTail, logp) {
                 return qnorm(mu, sigma, lowerTail, logp)(p);
              },
              r: function() { return rnorm(mu, sigma)(); }
           };
        }