class Eq < Type;

class Ord < Eq;

type a : Ord;

op f : forall e : Ord . e -> e;

op c : a;

. f (f c) = c

type t : Eq;

op b : t;

. f b = b

%% Classes ---------------------------------------------------------------

Eq < Type

Ord < Eq

%% Type Constructors -----------------------------------------------------

a : Ord

t : Eq

%% Assumptions -----------------------------------------------------------

b : t %(op)%

c : a %(op)%

f : forall e : Ord . e -> e %(op)%

%% Sentences -------------------------------------------------------------

f (f c) = c

f b = b

%% Diagnostics -----------------------------------------------------------

### Hint 16.3, constrain 't : Ord' is unprovable

known kinds are: Eq

*** Error 16.3, in term '(op f[t] : forall e : Ord . e -> e) (op b : t) = (op b : t)' of type 'Unit'

unresolved constraints '{t : Ord}'