error: return types are denoted using `->`
  --> $DIR/not-a-pred.rs:1:26
   |
LL | fn f(a: isize, b: isize) : lt(a, b) { }
   |                          ^
   |
help: use `->` instead
   |
LL | fn f(a: isize, b: isize) -> lt(a, b) { }
   |                          ~~

error[E0573]: expected type, found function `lt`
  --> $DIR/not-a-pred.rs:1:28
   |
LL | fn f(a: isize, b: isize) : lt(a, b) { }
   |                            ^^^^^^^^ not a type

error[E0573]: expected type, found local variable `a`
  --> $DIR/not-a-pred.rs:1:31
   |
LL | fn f(a: isize, b: isize) : lt(a, b) { }
   |                               ^ not a type

error[E0573]: expected type, found local variable `b`
  --> $DIR/not-a-pred.rs:1:34
   |
LL | fn f(a: isize, b: isize) : lt(a, b) { }
   |                                  ^ not a type

error[E0425]: cannot find function `check` in this scope
  --> $DIR/not-a-pred.rs:12:5
   |
LL |     check (lt(a, b));
   |     ^^^^^ not found in this scope

error: aborting due to 5 previous errors

Some errors have detailed explanations: E0425, E0573.
For more information about an error, try `rustc --explain E0425`.