No Annotations
∀[X:Type]. ∀[x,y,z:free-word(X)]. (x + y + z = x + y + z ∈ free-word(X))
{ (Auto THEN (Subst' x + y + z ~ x + y + z 0 THENM Auto)) }
.....equality.....
1. X : Type
2. x : free-word(X)
3. y : free-word(X)
4. z : free-word(X)
⊢ x + y + z ~ x + y + z