more complete simpset for linear arithmetic to avoid warnings: terms such as (2x + 2y)/2 can then be simplified by the linear arithmetic prover during its proof replay
--- a/src/HOL/Rat.thy Tue Aug 16 20:54:37 2016 +0200
+++ b/src/HOL/Rat.thy Wed Aug 17 10:23:49 2016 +0200
@@ -655,6 +655,7 @@
@{thm divide_1}, @{thm divide_zero_left},
@{thm times_divide_eq_right}, @{thm times_divide_eq_left},
@{thm minus_divide_left} RS sym, @{thm minus_divide_right} RS sym,
+ @{thm add_divide_distrib}, @{thm diff_divide_distrib},
@{thm of_int_minus}, @{thm of_int_diff},
@{thm of_int_of_nat_eq}]
#> Lin_Arith.add_simprocs [Numeral_Simprocs.field_divide_cancel_numeral_factor]