   function plnorm(meanlog, sdlog, lowerTail, logp) {
      var pnorm;

      lowerTail = lowerTail !== false;
      logp = logp === true;

      if (utils.hasNaN(meanlog, sdlog) || sdlog < 0) {
         return function() { return NaN; };
      }

      pnorm = normal.pnorm(meanlog, sdlog, lowerTail, logp);

      return function(x) {
         if (utils.hasNaN(x)) { return NaN; }
         if (x <= 0) {
            return lowerTail ? logp ? -Infinity : 0
                             : logp ? 0 : 1;
         }

         return pnorm(Math.log(x));
      };
   }