docs: function ppois(lambda, lowerTail, logp) {
        lowerTail = lowerTail !== false;
        logp = logp === true;
  
        if (!(lambda >= 0)) { return function(x) { return NaN; }; }
  
        return function(x) {
           if (utils.hasNaN(x)) { return NaN; }
           if (x < 0) { return utils.adjustLower(0, lowerTail, logp); }
           if (lambda === 0 || x === Infinity) {
              return utils.adjustLower(1, lowerTail, logp);
           }
  
           return pgamma(Math.floor(x + 1e-10) + 1, 1, !lowerTail, logp)(lambda);
        };
     }