egison-3.7.0: lib/math/geometry/minkowski-space.egi

(define $coordinates {t x y z})

(define $metric
  (generate-tensor
    (match-lambda [integer integer]
      {[[,1 ,1] -1]
       [[$n ,n] 1]
       [[_ _] 0]})
    {4 4}))

(define $.
  (lambda [$