infer-type-definition := λ(: base-type Type)(: body AST)(: case-number U64). (: (
   # This works but is too slow
   # (add-alias( '.tag_s '.0_s (t3( 'Arrow_s base-type (t1 'U64_s) )) ))
   (mark-class-exists( (tag-of base-type) ))
   (let r 0_u64)
   (match body (
      ()
      ( (App( (App( tds (Var( '|_s _ )) )) case )) (
         (let r1 (infer-type-definition( base-type tds (+( case-number 1_u64 )) )))
         (let r2 (infer-type-constructor( base-type case )))
         (set r (max( r1 r2 )))
      ))
      ( case (
         (set r (infer-type-constructor( base-type case )))
         (if (==( case-number 0_u64 )) (
            (let tag '_s)
            (match case (
               ()
               ( (Lit( tg _ )) (set tag tg) )
               ( (App( (Lit( tg _ )) args )) (set tag tg) )
               ( _ () )
            ))
            (if (head-string tag) (
               (match base-type (
                  ()
                  ( (TGround( cls _ )) (
                     (has-only-child( cls tag ))
                  ))
               ))
            ) ())
         ) ())
      ))
   ))
   r
) U64);