CAD sketches for Computer-Aided Design as Language : missing constraint reference to entity relationship

Hi,
I try to explore the dataset used by used in ["Computer-Aided Design as Language"](https://arxiv.org/abs/2105.02769), but I have problem in finding which entities each constraints refer to. For example, I try to retrieve the first sketch from the training split and I get the following entities and constraints:
```
entity_sequence {
entities {
line_entity {
start {
x: -0.9999989999620049
y: 0.14356660975133936
}
end {
x: -0.10311290613999784
y: 0.14356660975133936
}
}
}
entities {
line_entity {
start {
x: -0.10311290613999806
y: 0.14356660975133936
}
end {
x: -0.10311290613999806
y: 0.020326325688445626
}
}
}...}

constraint_sequence {
constraints {
coincident_constraint {
entities: 4
entities: 2
}
}
constraints {
coincident_constraint {
entities: 15
entities: 13
}
}
constraints {
coincident_constraint {
entities: 18
entities: 16
}
}...}
```
I wonder how these "entities" field in constrint corresponds to entities defined in above. For example, how the entities 2 and 4 in the first constraints corresponds to entities. I suspect these numbers refer to the index of entities or part of entities defined above, but in what way? Is there a reliable way to find out which entities/parts these constraints refer to?