This is a function in the [d3.v3.js](http://d3js.org/d3.v3.js) file ([the graph library D3.js](http://en.wikipedia.org/wiki/D3js)):

```
  function d3_geo_areaRingStart() {
    var λ00, φ00, λ0, cosφ0, sinφ0;
    d3_geo_area.point = function(λ, φ) {
      d3_geo_area.point = nextPoint;
      λ0 = (λ00 = λ) * d3_radians, cosφ0 = Math.cos(φ = (φ00 = φ) * d3_radians / 2 + π / 4), 
      sinφ0 = Math.sin(φ);
    };
    function nextPoint(λ, φ) {
      λ *= d3_radians;
      φ = φ * d3_radians / 2 + π / 4;
      var dλ = λ - λ0, cosφ = Math.cos(φ), sinφ = Math.sin(φ), k = sinφ0 * sinφ, u = cosφ0 * cosφ + k * Math.cos(dλ), v = k * Math.sin(dλ);
      d3_geo_areaRingSum.add(Math.atan2(v, u));
      λ0 = λ, cosφ0 = cosφ, sinφ0 = sinφ;
    }
    d3_geo_area.lineEnd = function() {
      nextPoint(λ00, φ00);
    };
  }

```

I was completely taken aback that the programmers used π, φ and λ as variable names. Surprisingly, these variables were accepted even by Notepad (ie: it didn't turn into junk/unrecognized characters).  

Is it good practice to use such variables? I can see that they're very intuitive and searchable too, but a bit unnerving.