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Mehretu is one of my all-time favorite painters, it's easy to see why.
I've had the pleasure of viewing her work first-hand at MoMA, and it's scale is very important... her work is huge.
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work in progress by matt boyle
Sadly, he died in poverty, "his last recorded words being a request to the bailiffs that they would not carry away the bed on which he was dying." - wikipedia
Here is a great collection of his works from the University of Toronto.