Reversal is an involution

NOT A NOVELTY CLAIM. This is a machine-checked formalisation, decided by the Lean 4 kernel and depending on no axiom. It is dated and citable. Prior art, where it exists, is cited below. No discovery is claimed.

T² = id. Reversing time twice returns the equation, whatever the viscosity.

Proposition

T (T navierStokes) = navierStokes ∧ T (T euler) = euler

Proof

By decide in navier-stokes.lean. The kernel reduces the proposition and reports no axiom dependency.

Sources and identifiers

• Lean source · src/pair/formal/proofs/navier-stokes.lean
• Typeset paper · src/research/lean-theorems.tex
• Repository deposit · doi:10.5281/zenodo.21787144
• Author · ORCID 0009-0000-7312-9778
• Deposit record · navier-stokes--reversal_is_an_involution

Proved in the same file

• Euler is time reversible
• Viscosity breaks time reversal
• Fixed points are exactly the inviscid

All machine-checked theorems