Try doing some basic maths questions in the Lean Theorem Prover. Functions, real numbers, equivalence relations and groups. Click on README.md and then on "Open in CoCalc with one click".
License: APACHE
import data.set.basic
open set
def equivalence_class {X : Type} (R : X → X → Prop) (x : X) := {y : X | R x y}
example (X : Type) (R : X → X → Prop) (hR : equivalence R) (x : X) : equivalence_class R x ≠ ∅ :=
begin
rw ne_empty_iff_exists_mem,
use x,
cases hR with hR H,
exact hR x,
end