metaphisical question. Reviewed-by does also imply Acked-by?
yes
I'd say it depends
some people consider that Rb is stronger than Ab, other people think the other way around
To me: RB means "I've checked this code, and see no bugs, and I'm happy for it to be merged" ... AB: means "I haven't specifically reviewed this - but I believe it should be merged for $WHATEVER_REASONS"
kbingham: that's who I understand it too and in line with what's documented in Documentation/process/submitting-patches.rst
that's how I interpret it, but I know that for some people Rb means "I've reviewed the patch and it looks fine to me", while Ab means "I put my reputation at stake and say we should merge this"
pinchartl: yeah and at least what I usually do is to use Ab if the changes is for code I maintain and use Rb when I reviewed the patch but is not for code I maintain 
that is, use Ab to say "I think is OK to merge this patch" 
I use Ab to say "no objection but I'm no expert on this", and Rb to give my real stamp of full approval
pinchartl: I see
pinchartl: so for you Rb implies Ab 
for me yes
but not the other way around 
I think the problem is that Ab doesn't tell how much the person doing the ack reviewed the code 
Rb certainly implies the person has reviewed the patch, yes
pinchartl: exactly and then would imply an ack 
I always use it as a if ack implied rb but I see now that this may not be the case 
s/now// actually since I knew it but never gave that much thought 
I interpret r-b and a-b the same way pinchartl does. r-b is in-depth, a-b is 'whatever, I'm OK with it', or possibly 'I quickly scanned it and it looks OK to me'.
hverkuil, pinchartl: thanks for your insights, very useful