[Agda] 1-infix-2

[Sergei Meshveliani]

Can anyone tell, please,

is it possible to apply a relation  ~ : A → A → A → Set α
as 
    x ~ y z
?

I try

_~_⟶_ :  ∀ {α} {A : Set α} → A → A → A → Set α
_~_⟶_ x y z =  x ≢ y × x ≢ z

But I need the second line to be 
                              x ~ y z =  x ≢ y × x ≢ z       

And Agda reports  "Missing definition for _~_⟶_  ".
What is a way out?

Thanks,

------
Sergei