begin match sup, inf with
  | _, {kind = No_leaves} -> true
  | {kind = Mass_up ({cl_dist = sup_cl}, _)}, {kind = Mass_down {cl_dist = inf_cl}}
  | {kind = Mass_up ({cl_dist = sup_cl}, _)}, {kind = Mass_up ({cl_dist = inf_cl}, _)}
  | {kind = Mass_down {cl_dist = sup_cl}}, {kind = Mass_down {cl_dist = inf_cl}}
  | {kind = Mass_down {cl_dist = sup_cl}}, {kind = Mass_up ({cl_dist = inf_cl}, _)} ->
    sup_cl <= inf_cl
  | _, _ -> false