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Modify the logical relation judment to include an environment Δ that
contains a list of semantic types to interpret free type variables.

- Change the types in the examples slightly
- Use notations in the examples
- Modify some tactics to make the proofs more smooth

In the interpretation of recursive types

- Remove commented out code
- Pull std++ related lemmas into a separate file

Following the advice of Amin Timany
generalize all the compatibility lemmas
at the same time by declaring a mask E in a Section.

We are switich away from De Bruijn indices because
1) it's hard to read terms with De Bruijn indices
2) they are making lots of things slower

And improve the proof of the fundamental property

A new formulation allows for doing more work inside HOSL.

Γ ⊨ e ≤log≤ e' : τ <=>
∀ Δ vvs ρ,
  spec_ctx ρ -∗
  □ ⟦ Γ ⟧* Δ vvs -∗
  ⟦ τ ⟧ₑ Δ (e.[env_subst (vvs.*1)], e'.[env_subst (vvs.*2)])

Slightly generalize the way tac_tp_bind works and rewrite the
fundamental property for F_mu_ref_conc using tp_ tactics

sans examples

This reverts commit 15005661.

This reverts commit efe1b574.