FUNC y = Sqrt(x) IS 
  y ~ x / 10 AND y * y = x 
END;

FUNC len = Length(v) IS 
  (E vx, vy, len2 :: 
     v = (vx, vy) AND 
     len2 = (vx * vx) + (vy * vy) AND 
     len = Sqrt(len2)) 
END;