code: def blend_value(data, i, j, k, keys=None):
      
  
      key_size = len(list(data.keys())[0])
      if not keys:
          keys = triangle_coordinates(i, j, k)
      # Reduce key from (i, j, k) to (i, j) if necessary
      keys = [tuple(key[:key_size]) for key in keys]
  
      # Sum over the values of the points to blend
      try:
          s = sum(data[key] for key in keys)
          value = s / 3.
      except KeyError:
          value = None
      return value
docs: Computes the average value of the three vertices of a triangle in the
      simplex triangulation, where two of the vertices are on the lower
      horizontal.