This function converts an internally processed equation expression (e.g., `m[.i, 'Var']`) into a more readable format (e.g., `Var`). The function handles lagged variables, transforming expressions such as `m[.i - 1, 'Var']` into `Var[-1]`. It is intended for use in warning messages.
restore_equation(eq_line)A character string where the internal indexing notation has been restored to a more user-friendly form.
A character string representing an equation with internal indexing.