sentences:  In practice, formula_10 is estimated from the database of known protein
  structures, while formula_18 typically results from calculations
  or simulations.For example, formula_10 could be the conditional probability
  of finding the formula_20 atoms of a valine and a serine at a given
  distance formula_3 from each other, giving rise to the free energy difference
  formula_22.The total free energy difference of a protein,
  formula_23, is then claimed to be the sum
  of all the pairwise free energies