simp [Fintype.card_subtype_compl, card_topic, Topic']
Person Topic : Type
inst✝³ : Fintype Person
inst✝² : DecidableEq Person
inst✝¹ : Fintype Topic
inst✝ : DecidableEq Topic
card_person : 5 < Fintype.card Person
card_topic : Fintype.card Topic = 2
discusses : Person → Person → Topic
discussion_sym : ∀ (p1 p2 : Person), discusses p1 p2 = discusses p2 p1
p2 : Person
Person' : Type := { p3 // p3 ≠ p2 }
hfcα : 4 < Fintype.card Person'
h1 : Fintype.card Topic * 2 < Fintype.card Person'
t2 : Topic
ht2 : 2 < (Finset.filter (fun x => (fun p3 => discusses p2 ↑p3) x = t2) Finset.univ).card
α : Finset Person' := Finset.filter (fun x => discusses p2 ↑x = t2) Finset.univ
Topic' : Type := { t3 // t3 ≠ t2 }
⊢ Fintype.card Topic' = 1
no goals