function distance(f1_φ, f1_λ, f2_φ, f2_λ) {
  return 2 * asin(sqrt(
      pow(sin((f1_φ - f2_φ) / 2), 2) +
      cos(f1_φ) * cos(f2_φ) * pow(sin((f1_λ - f2_λ) / 2), 2)
    ));
}
function distance(f1_φ, f1_λ, f2_φ, f2_λ) {
  return 2 * asin(sqrt(
      pow(sin((f1_φ - f2_φ) / 2), 2) +
      cos(f1_φ) * cos(f2_φ) * pow(sin((f1_λ - f2_λ) / 2), 2)
    ));
}
function distance ( f1_φ, 1_λ,  f _φ, f 2 λ) { return 2 * asin ( sqrt ( pow ( sin ( ( f1_φ  2_φ)  / 2 , 2 + cos ( f1_φ) os( f 2_φ)  * p w(s i n(( f 1 _λ -  2 λ) /  2 , 2 ) ) ) ; }
the spherical arclength of the icosahedron's edges. 
Returns the arc length between two positions.

@return {number} arc length
the spherical arclength of the icosahedron s edges . Returns the arc length between two positions .