Lean Kernel Arena / bugs/level-imax-normalization

Proof of False via incorrect universe level normalization for imax.

A correct kernel must distinguish imax 0 v from succ(imax 0 v), since at v=0 these evaluate to 0 and 1 respectively. However, a level normalization algorithm that drops an accumulated successor offset when decomposing imax u (param v) will produce identical normal forms for both, causing the equivalence check to incorrectly return true.

This allows defining a universe-collapsing identity function down.{v} : Sort (succ (imax 0 v)) → Sort (imax 0 v), and then myProp : Prop := down.{0} Bool (a Prop that is computationally Bool). Proof irrelevance on myProp equates Bool.true and Bool.false, and Bool.rec maps this into False.