Revert "stub for lambda_lift()"

This reverts commit 7da8e17204fc103b5a85cdd29321671600e989e1.
Revert "differentiate local and non-local references for later lambda-lifting"

This reverts commit 17b28c291cf7a554b34a6e996ee19323e26b7054.
Revert "Revert "add support for nested scopes""

This reverts commit 97caaa8772a6f98e0546693b4eb88c90f44181a5.
Revert "add support for nested scopes"

This reverts commit 17dddd7dc1fe3119e3d3c7315be0066acb19e14b.
Revert "simple id-lookup"

This reverts commit 70e9f2748fc52a80fbeb0922a60e9dbd6b6e3c89.