Allow duplicate names of reduced/repeated dims

[AntonOresten]

If I want to do k inner repeats along two dims, currently I'd do:

repeat(x, einops"L1 L2 -> (k2 L1) (k2 L2)", k1=k, k2=k)

But it would make sense if one could write:

repeat(x, einops"L1 L2 -> (k L1) (k L2)", k=k)

[AntonOresten]

It's more straight-forward for repeat than reduce, as reduce requires dimension size consistency checks.