I defined a new type (`Mod29`

– integers mod 29).

```
struct Mod29 <: Real
value::Int8
function Mod29(value::Integer)
new(Int8(mod(value, 29)))
end
end
```

In another, generic, algorithm, I need to know whether comparison is defined on a type. I did not define comparison on `Mod29`

, and indeed `Mod29(1) < Mod29(3)`

fails:

```
**julia>** Mod29(1) < Mod29(3)
**ERROR:** < not defined for Mod29
Stacktrace:
[1] **error(** ::String, ::String, ::Type **)** at **./error.jl:42**
[2] **no_op_err(** ::String, ::Type **)** at **./promotion.jl:410**
[3] **<(** ::Mod29, ::Mod29 **)** at **./promotion.jl:426**
[4] top-level scope at **none:0**
```

But `hasmethod(<, (Mod29, Mod29))`

and `hasmethod(isless, (Mod29, Mod29))`

both return `true`

.

I see that `<`

and `isless`

fail trying to do promotion, but I don’t see how to tell that ‘<’ will fail, without trying it and catching the error.

For your amusement, the algorithm I need to change is LU decomposition, where it tries to pivot on the max. If comparison isn’t defined, I just want it to find an element with an inverse, to pivot on. I want to be able to take inverses of matrices of modular numbers.