mathlib

3baad3bf - feat(model_theory/syntax): Swapping between constants and variables (#14018)

feat(model_theory/syntax): Swapping between constants and variables (#14018) `term.constants_vars_equiv` and `bounded_formula.constants_vars_equiv` send terms/formulas with constants to terms/formulas with extra variables and back. Co-authored-by: Rob Lewis <Rob.y.lewis@gmail.com>