diff --git a/TODO.org b/TODO.org
index 0c205182..13ed389d 100644
--- a/TODO.org
+++ b/TODO.org
@@ -10,6 +10,9 @@ pointing at it. A CANCELLED entry carries the one-line reason, because an idea
 rejected without a record is an idea that gets re-proposed.
 
 * Language surface
+** CANCELLED rand-int returns i64
+Decided 2026-09-26 (134): rand-int stays u64; write rand-int-range(lo, hi) for a signed
+range.
 ** DONE A literal's reading is fixed where it is bound
 CLOSED: [2026-09-26]
 Decision 132, clarifying 117: a vector, map or text literal is typed only when its own
@@ -801,9 +804,14 @@ One spelling for one operation; != stays, and not= is refused with a suggestion
 of !=.
 
 * Checker
-** TODO A dyn operand past the second in a + fold is converted to the running type
-=(+ 1 2 d)= with d a dyn char prints 100: the dyn is unboxed to i32 before adding, where
-rule 117 says typed beside dyn gives dyn (=(+ 3 d)= gives =\d=). Predates the char lane.
+** TODO A u64 above the i64 maximum becomes -1 when it crosses into dyn
+=(+ z u)= and =(max u 0 z)= with u = u64 max read u as -1, silently. It should trap at
+the crossing, as a u64 field read through a view already does.
+** TODO A dyn nil past the first pair of a fold is refused at compile time
+=(+ 1 2 (the dyn nil))= says nil has no None at i32, while =(+ (the dyn nil) 1 2)= traps
+at run time. Both should trap at run time.
+** TODO A generic $t beside a dyn operand is refused
+"does not cross into a written type yet"; rule 117 says typed beside dyn gives dyn.
 ** WAIT Checking a wide fold of let operands is slow
 Parked 2026-09-26: design first; remeasure on a quiet machine, it was timed under load 20.
 A 2000-operand (bit-and (let …) …) takes 32 s to check (37 s before the bit operators);
diff --git a/lib/check.ml b/lib/check.ml
index 9bb94eb6..48360e96 100644
--- a/lib/check.ml
+++ b/lib/check.ml
@@ -11805,21 +11805,30 @@ and fold_left_prim ctx ~want loc name p ~needs ok what args =
     (* Left to right, each step char arithmetic when a char is in it and the
        ordinary join when none is: (- \z \a 1) is 25 - 1, and (+ 1 2 \a) is
        3 + \a. *)
-    let step acc (arg : Ast.expr) =
-      let lit = char_lit arg in
-      untyped := !untyped && int_lit arg;
-      if is_char acc || maybe_char ctx arg || lit then
-        let v = check ctx arg in
-        if is_char acc || is_char v then char_step ~want:nwant loc name acc v
-        else mk loc acc.Tast.ty (Tast.Prim (p, [ acc; expect ctx arg.Ast.loc ~want:(Some acc.Tast.ty) v ]))
-      else
-        mk loc acc.Tast.ty (Tast.Prim (p, [ acc; check ctx ~want:acc.Tast.ty arg ]))
+    let rec steps acc = function
+      | [] -> expect ctx loc ~want acc
+      | (arg : Ast.expr) :: tl ->
+        let lit = char_lit arg in
+        untyped := !untyped && int_lit arg;
+        if is_char acc || maybe_char ctx arg || lit then
+          let v = check ctx arg in
+          if v.Tast.ty = Types.Dyn then dyn_fold ctx ~want loc name [ acc; v ] tl
+          else if is_char acc || is_char v then
+            steps (char_step ~want:nwant loc name acc v) tl
+          else
+            match fold_operand ctx acc.Tast.ty (expect ctx arg.Ast.loc ~want:(Some acc.Tast.ty) v) with
+            | `Typed v -> steps (mk loc acc.Tast.ty (Tast.Prim (p, [ acc; v ]))) tl
+            | `Dyn d -> dyn_fold ctx ~want loc name [ acc; d ] tl
+        else
+          match fold_operand ctx acc.Tast.ty (check ctx ~want:acc.Tast.ty arg) with
+          | `Typed v -> steps (mk loc acc.Tast.ty (Tast.Prim (p, [ acc; v ]))) tl
+          | `Dyn d -> dyn_fold ctx ~want loc name [ acc; d ] tl
     in
     let first =
       if is_char a || is_char b then char_step ~want:nwant loc name a b
       else mk loc a.Tast.ty (Tast.Prim (p, [ a; b ]))
     in
-    expect ctx loc ~want (List.fold_left step first rest)
+    steps first rest
   else if a.Tast.ty = Types.Dyn || b.Tast.ty = Types.Dyn then
     dyn_fold ctx ~want loc name [ a; b ] rest
   else begin
@@ -11835,16 +11844,27 @@ and fold_left_prim ctx ~want loc name p ~needs ok what args =
      answered again, per copy, at the instantiation. *)
   if not (ok a.Tast.ty || generic_ty a.Tast.ty) then not_numeric name what a;
   let ty = a.Tast.ty in
-  let acc =
-    List.fold_left
-      (fun acc arg ->
-         mk loc ty (Tast.Prim (p, [ acc; check ctx ~want:ty arg ])))
-      (mk loc ty (Tast.Prim (p, [ a; b ])))
-      rest
+  let rec steps acc = function
+    | [] -> expect ctx loc ~want acc
+    | arg :: tl ->
+      match fold_operand ctx ty (check ctx ~want:ty arg) with
+      | `Typed v -> steps (mk loc ty (Tast.Prim (p, [ acc; v ]))) tl
+      | `Dyn d -> dyn_fold ctx ~want loc name [ acc; d ] tl
   in
-  expect ctx loc ~want acc
+  steps (mk loc ty (Tast.Prim (p, [ a; b ]))) rest
   end
 
+(* An operand past a fold's first pair, checked at the type so far. A dyn one
+   is taken back as the dyn it was, not opened at that type: a typed operand
+   beside a dyn gives dyn (rule 117), so from there on the fold is the dyn
+   runtime's, and (+ 1 2 d) is (+ 3 d). *)
+and fold_operand ctx ty (v : Tast.expr) =
+  if v.Tast.ty = Types.Dyn && not (Types.equal ty Types.Dyn) then `Dyn v
+  else
+    match opened_dyn ~box:(to_dyn ctx) v with
+    | Some d -> `Dyn d
+    | None -> `Typed v
+
 (* A pair an arithmetic operator refused, when one operand is a char: that
    is the refusal to give, rather than the mismatch between the two. Asked
    only after the refusal, so a pair that checks costs nothing more. *)
@@ -11941,11 +11961,12 @@ and dyn_fold ctx ~want loc name first rest =
     | "+" -> "flan_dyn_add" | "-" -> "flan_dyn_sub"
     | "*" -> "flan_dyn_mul" | "/" -> "flan_dyn_div"
     | "%" -> "flan_dyn_rem"
+    | "min" -> "flan_dyn_min" | "max" -> "flan_dyn_max"
     | _ -> dyn_bits_sym name
   in
   (* A bitwise fold takes integers on both sides, and the typed side of a
      mixed pair can be asked now rather than at run time. *)
-  let bitwise = not (List.mem name [ "+"; "-"; "*"; "/"; "%" ]) in
+  let bitwise = not (List.mem name [ "+"; "-"; "*"; "/"; "%"; "min"; "max" ]) in
   if bitwise then
     List.iter
       (fun (v : Tast.expr) ->
@@ -13416,7 +13437,8 @@ and named_call ?(qualified = false) ctx ~want loc name args =
        two things being unalike is the answer to "are these equal", not an
        error. The orderings do trap, and rightly — there is no true answer to
        whether a string is less than a vector. *)
-    if a.Tast.ty = Types.Dyn || b.Tast.ty = Types.Dyn then begin
+    (* [ops] are every operand, boxed. *)
+    let dyn_chain ops =
       let sym =
         match name with
         | "=" | "!=" -> "flan_dyn_eq"
@@ -13443,15 +13465,15 @@ and named_call ?(qualified = false) ctx ~want loc name args =
       let r =
         match rest with
         | [] -> link (box loc a) (box loc b)
-        | _ ->
-          let ops =
-            box loc a :: box loc b
-            :: map_lr (fun e -> box loc (check ctx ~want:Types.Dyn e)) rest
-          in
-          cmp_over ctx loc Types.Dyn ~pairs ~link ops
+        | _ -> cmp_over ctx loc Types.Dyn ~pairs ~link (ops ())
       in
       expect ctx loc ~want r
-    end else begin
+    in
+    if a.Tast.ty = Types.Dyn || b.Tast.ty = Types.Dyn then
+      dyn_chain (fun () ->
+          box loc a :: box loc b
+          :: map_lr (fun e -> box loc (check ctx ~want:Types.Dyn e)) rest)
+    else begin
     (* [=] and [!=] admit types [<] does not. A handle is one: a pair of
        numbers in one word and where being the same entity is the question the
        type exists to answer — ordering handles would order a slot index,
@@ -13486,8 +13508,18 @@ and named_call ?(qualified = false) ctx ~want loc name args =
     | _ ->
       let ty = a.Tast.ty in
       let link u v = mk loc Types.Bool (Tast.Prim (p, [ u; v ])) in
-      let ops = a :: b :: map_lr (fun e -> check ctx ~want:ty e) rest in
-      expect ctx loc ~want (cmp_over ctx loc ty ~pairs ~link ops)
+      let rest = map_lr (fun e -> fold_operand ctx ty (check ctx ~want:ty e)) rest in
+      (* A dyn past the first pair makes the whole chain the dyn runtime's,
+         for [fold_operand]'s reason: a chain is its pairs, and a pair with a
+         dyn in it is a dyn comparison. *)
+      if List.exists (function `Dyn _ -> true | `Typed _ -> false) rest then
+        dyn_chain (fun () ->
+            box loc a :: box loc b
+            :: List.map (function `Dyn d -> d | `Typed v -> box loc v) rest)
+      else
+        let ops =
+          a :: b :: List.map (function `Typed v -> v | `Dyn d -> d) rest in
+        expect ctx loc ~want (cmp_over ctx loc ty ~pairs ~link ops)
     end
   | "not" ->
     arity ctx loc name 1 args;
@@ -13598,7 +13630,10 @@ and named_call ?(qualified = false) ctx ~want loc name args =
     let x, y, rest =
       match args with x :: y :: rest -> x, y, rest | _ -> assert false
     in
-    let a, b = binary ctx name loc ~want:(numeric_want want) [ x; y ] in
+    let a, b = binary ctx ~dyn_ok:true name loc ~want:(numeric_want want) [ x; y ] in
+    if a.Tast.ty = Types.Dyn || b.Tast.ty = Types.Dyn then
+      dyn_fold ctx ~want loc name [ a; b ] rest
+    else begin
     (* [min] and [max] are [<] with a pick, so [is-ordered] is what they want —
        not [is-numeric]. A generic that declares [is-ordered] gets both.
 
@@ -13625,9 +13660,15 @@ and named_call ?(qualified = false) ctx ~want loc name args =
       mk loc ty (Tast.Let ([ (sa, a); (sb, b) ],
                            [ mk loc ty (Tast.If (test, la, lb)) ]))
     in
-    expect ctx loc ~want
-      (List.fold_left (fun acc arg -> pick acc (check ctx ~want:ty arg))
-         (pick a b) rest)
+    let rec steps acc = function
+      | [] -> expect ctx loc ~want acc
+      | arg :: tl ->
+        match fold_operand ctx ty (check ctx ~want:ty arg) with
+        | `Typed v -> steps (pick acc v) tl
+        | `Dyn d -> dyn_fold ctx ~want loc name [ acc; d ] tl
+    in
+    steps (pick a b) rest
+    end
   (* A type handed to the prelude's slice reductions: the reach for the
      type-limit constants under the name of the reduction beside them. *)
   | ("max-of" | "min-of")
diff --git a/lib/emit.ml b/lib/emit.ml
index 718c5be7..12bf55ca 100644
--- a/lib/emit.ml
+++ b/lib/emit.ml
@@ -5117,6 +5117,8 @@ declare i64 @flan_dyn_lt(i64, i64, ptr, i64)
 declare i64 @flan_dyn_le(i64, i64, ptr, i64)
 declare i64 @flan_dyn_gt(i64, i64, ptr, i64)
 declare i64 @flan_dyn_ge(i64, i64, ptr, i64)
+declare i64 @flan_dyn_min(i64, i64, ptr, i64)
+declare i64 @flan_dyn_max(i64, i64, ptr, i64)
 declare i64 @flan_dyn_eq(i64, i64)
 declare i64 @flan_dyn_len(i64)
 declare i64 @flan_dyn_eq_at(i64, i64, ptr, i64)
diff --git a/runtime/flan_dyn.c b/runtime/flan_dyn.c
index 12ec2950..d3c8fcbf 100644
--- a/runtime/flan_dyn.c
+++ b/runtime/flan_dyn.c
@@ -3382,6 +3382,30 @@ flan_dyn flan_dyn_ge(flan_dyn a, flan_dyn b, const uint8_t *loc,
   return flan_dyn_from_bool(c == 1 || c == 0);
 }
 
+/* The pick of min and max: numbers by value, keeping the one picked as it is
+ * (an int stays an int), and chars by code point. Anything else traps, text
+ * included, since min over text has no typed counterpart. The first is picked
+ * only when it is strictly less (or greater), so a tie or a NaN answers the
+ * second, as the typed (if (< a b) a b) does. */
+static flan_dyn pick(const uint8_t *loc, int64_t loclen, const char *op,
+                     flan_dyn a, flan_dyn b, int want) {
+  int both_chars = flan_dyn_tag(a) == FLAN_DYN_TAG_CHAR &&
+                   flan_dyn_tag(b) == FLAN_DYN_TAG_CHAR;
+  if (!both_chars && !(is_num(a) && is_num(b)))
+    trap2(loc, loclen, TYPE_TRAP, op,
+          "it picks between two numbers or two chars, and these are neither",
+          a, b);
+  return order(loc, loclen, op, a, b) == want ? a : b;
+}
+flan_dyn flan_dyn_min(flan_dyn a, flan_dyn b, const uint8_t *loc,
+                      int64_t loclen) {
+  return pick(loc, loclen, "min", a, b, -1);
+}
+flan_dyn flan_dyn_max(flan_dyn a, flan_dyn b, const uint8_t *loc,
+                      int64_t loclen) {
+  return pick(loc, loclen, "max", a, b, 1);
+}
+
 /* ── Equality ──────────────────────────────────────────────────────────
  *
  * Structural, and the only operation here that never traps: two values of
diff --git a/runtime/flan_dyn.h b/runtime/flan_dyn.h
index 2595b756..e7399cca 100644
--- a/runtime/flan_dyn.h
+++ b/runtime/flan_dyn.h
@@ -231,6 +231,11 @@ flan_dyn flan_dyn_le(flan_dyn a, flan_dyn b, const uint8_t *loc, int64_t loclen)
 flan_dyn flan_dyn_gt(flan_dyn a, flan_dyn b, const uint8_t *loc, int64_t loclen);
 flan_dyn flan_dyn_ge(flan_dyn a, flan_dyn b, const uint8_t *loc, int64_t loclen);
 
+/* Answer whichever of a and b is less (min) or greater (max), b on a tie:
+ * numbers by value, chars by code point; anything else traps. */
+flan_dyn flan_dyn_min(flan_dyn a, flan_dyn b, const uint8_t *loc, int64_t loclen);
+flan_dyn flan_dyn_max(flan_dyn a, flan_dyn b, const uint8_t *loc, int64_t loclen);
+
 /* Structural, and the one operation in this file that never traps: two values
  * of unrelated tags are not an error, they are unequal. */
 flan_dyn flan_dyn_eq(flan_dyn a, flan_dyn b);
diff --git a/test/programs/dyn-fold-position.flan b/test/programs/dyn-fold-position.flan
new file mode 100644
index 00000000..a485509f
--- /dev/null
+++ b/test/programs/dyn-fold-position.flan
@@ -0,0 +1,47 @@
+;;;; A dyn operand anywhere in a fold makes the fold dyn from there on: the
+;;;; typed operands before it are folded typed, and the dyn runtime takes the
+;;;; rest. (+ 1 2 d) is (+ 3 d), whichever position the dyn is in.
+
+(defn as-i32 [x i32] i32 x)
+(defn as-f64 [x f64] f64 x)
+
+(defn loud [x i32] i32 (println "i" x) x)
+(defn loud-dyn [x dyn] dyn (println "d" x) x)
+
+(defn main [args [str]] i32
+  (let [d (the dyn \a)
+        f (the dyn 2.5)
+        n (the dyn 4)
+        c \a]
+    ;; + and - over a dyn char: first, middle, last.
+    (println (+ d 1 2) (+ 1 d 2) (+ 1 2 d))
+    (println (- d 1 2) (- 10 n 1) (- 10 1 n))
+    ;; A dyn float past an integer pair promotes, as (* 6 f) does.
+    (println (* f 2 3) (* 2 f 3) (* 2 3 f))
+    (println (/ f 2 5) (/ 9 f 2) (/ 9 2 f))
+    (println (+ 1 2 3 f) (- 10 1 2 f))
+    ;; A char fold with a dyn past the pair.
+    (println (+ c 1 n) (- c 1 n) (+ c 1 2 n))
+    ;; The bitwise folds.
+    (println (bit-or n 1 2) (bit-or 1 n 2) (bit-or 1 2 n))
+    (println (bit-and n 7 6) (bit-and 7 n 6) (bit-and 7 6 n))
+    (println (bit-xor n 1 2) (bit-xor 1 n 2) (bit-xor 1 2 n))
+    ;; Comparison chains: a float past an integer pair is compared as one.
+    (println (< f 3 4) (< 1 f 3) (< 1 2 f) (< 1 3 f))
+    (println (<= 2 2 f) (> 3 2 f) (>= 3 3 f) (>= 3 3 n))
+    (println (= 4 4 n) (= 4 n 4) (= n 4 4) (= 4 4 f))
+    (println (!= 1 2 n) (!= 1 4 n) (!= 2 f 3))
+    ;; min and max: numbers by value, the one picked kept as it is, and
+    ;; chars by code point.
+    (println (min f 3 4) (min 3 f 4) (min 3 4 f) (min 1 2 f))
+    (println (max n 1 2) (max 1 n 2) (max 1 2 n) (max 5 6 n))
+    (println (min d \c \b) (max \b d \c) (max \b \c d) (min 1.5 2.5 n))
+    ;; Each operand is evaluated once, left to right.
+    (println (min (loud 3) (loud 2) (loud-dyn n) (loud 1)))
+    (println (max (loud 3) (loud-dyn n) (loud 9)))
+    ;; With an argument, min over a number and a text traps at the form.
+    (when (> (length args) 1)
+      (println (min 1 2 (the dyn "a"))))
+    ;; At a typed want the dyn answer is opened at the end.
+    (println (as-i32 (+ 1 2 n)) (as-f64 (* 2 3 f))))
+  0)
diff --git a/test/test_acceptance.ml b/test/test_acceptance.ml
index 4f986296..1233fb1c 100644
--- a/test/test_acceptance.ml
+++ b/test/test_acceptance.ml
@@ -5638,6 +5638,33 @@ level "1"
       char_arith_out;
     outputs ~x86:true "char: arithmetic, --x86" "programs/char-arith.flan"
       char_arith_out;
+    (* A dyn anywhere in a fold makes it dyn from there on (rule 117): each
+       family with the dyn first, in the middle and last. *)
+    let fold_out =
+      "d d d\n^ 5 5\n15 15 15\n0.25 1.8 1.6\n8.5 4.5\nf \\ h\n7 7 7\n\
+       4 4 4\n7 7 7\ntrue true true false\ntrue false true false\n\
+       true true true false\ntrue false true\n2.5 2.5 2.5 1\n4 4 4 6\n\
+       a c c 1.5\ni 3\ni 2\nd 4\ni 1\n1\ni 3\nd 4\ni 9\n9\n7 15\n"
+    in
+    outputs "dyn: a dyn in any fold position" "programs/dyn-fold-position.flan"
+      fold_out;
+    outputs ~opt:"-O0" "dyn: a dyn in any fold position, -O0"
+      "programs/dyn-fold-position.flan" fold_out;
+    outputs ~x86:true "dyn: a dyn in any fold position, --x86"
+      "programs/dyn-fold-position.flan" fold_out;
+    List.iter
+      (fun x86 ->
+         let exe = compile ~x86 "programs/dyn-fold-position.flan" in
+         let code, text = run exe (Some "x") in
+         let want = "programs/dyn-fold-position.flan:44:16: dyn min: int and \
+                     text, and it picks between two numbers or two chars" in
+         if code <> 134 || not (contains text want) then begin
+           incr failures;
+           Printf.printf "FAIL  dyn: min over a number and a text traps%s\n        \
+                          got: %S (exit %d)\n"
+             (if x86 then ", --x86" else "") text code
+         end)
+      [ false; true ];
     List.iter
       (fun x86 ->
          let exe = compile ~x86 "programs/char-arith.flan" in