let user_default_label = function
| [] -> Clabels.Here
| LogicLabel (None, first) :: _ -> Clabels.LabelParam first
| LogicLabel (Some _, _) :: _ ->
Wp_parameters.fatal
"Unexpected redefined labels in user-defined predicates"
| StmtLabel _ :: _ ->
Wp_parameters.fatal
"Unexpected stmt-labels in user-defined predicates"