Explain time disadvantage of nested representation
Combine valid and size proofs for fromList into one proof.
Remove old commented-out code
More general application Ltac and simpler pushFront lemma definition.
A first small use of autorewrite
remove explicit matching on Lean in goal, in some cases
destroy lean variables when possible
Reove need to destruct discriminants in goal of type option
Simpler proofs in coq version of Braun streams