Some MTG may have missing vertices at the lower scale. ``` ENTITY-CODE /P /A1 2016 ^/S1 +B1 2017 +C1 2018 ``` C1 has no parents g.roots(scale=2) return [2, 4, 5]
Some MTG may have missing vertices at the lower scale.
C1 has no parents
g.roots(scale=2) return [2, 4, 5]