let label_of_kind = function
| PKProp -> "Property"
| PKPropLoop -> "Invariant" (* should be assert false ??? *)
| PKEstablished -> "Establishment"
| PKPreserved -> "Preservation"
| PKVarDecr -> "Decreasing"
| PKVarPos -> "Positive"
| PKAFctOut -> "Function assigns"
| PKAFctExit -> "Exit assigns"
| PKPre(kf,_,_) ->
Printf.sprintf "Precondition for '%s'" (Kernel_function.get_name kf)