title: Netlogo - selecting all turtles at a given distance from a special agent
body: <p>I have to select and compute the nearest turtle from a fixed point, however i want the distance to be changeable, in the sense that i have a slider and i want to select the nearest turtle with that 
   given distance from that point.
  I've tried many solution, also with the <code>in-radius</code> function, but it does not produce the desired output.
  Can anyone help me? thanks in advance.</p>