sentences:  formula_33 will be defined via the exponential map, its inverse, and a linear isometry between their tangent spaces, 
  
  That is 
  
  where formula_36.That is to say, the starting point formula_37 goes to the tangent plane from formula_20 through the inverse of the exponential map.Then travels from one tangent plane to the other through the isometry formula_39, and then down to the surface formula_6 with another exponential map.