Replace Array.exists by Array.fold_left

Array.exists is only available since OCaml 4.03.0 and we need to
support version at least version 4.02.3.

src/coalg/coalg.ml

@@ -94,9 +94,12 @@ let verbose = ref false
 let choiceSat () =
     let verb = !verbose in
     let sorts = (FE.sortTableFromString Sys.argv.(2)) in
-    if Array.exists (fun (func,_) -> func == CM.GML || func == CM.PML) sorts then
+
+    (* test if GML or PML occurs in sort table *)
+    if Array.fold_left (fun x (func,_) -> x || func == CM.GML || func == CM.PML) false sorts then
       raise (CF.CoAlgException "GML and PML are currently not supported")
     else ();
+
     let printRes sat =
       if not verb then
         print_endline (if sat then "satisfiable\n" else "unsatisfiable\n")