Basic HTML version of Foils prepared March 15 00
| In red-black, you color every alternate point red and every other point black |
| This gives a checkerboard pattern shown on previous foil |
| Now label update so first update all red points, then update all black points |
| Updating red points to iterate k only requires black points at level k-1 |
| Updating black points to level k requires NO black points but just read points at level k |
So can divide parallel update into two phases
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