I have downloaded the file "protein chemical.links.v4.0.tsv.gz" from STITCH 4.0. From the database, the chemical identifiers are described as below:

**Chemical identifiers are of the form CID123456789, where the number stands for the PubChem compound identifier of the merged compound**

Here are some example of chemical identifiers in the file :

```
CID171549452
CID171549315
CID171464722
```

However, I can't find the result in PubChem database by inputting the identifiers I obtain from the downloaded file. Can I know what are the problems behind and how can I solve this?
The description from STITCH is not entirely accurate. STITCH has two kinds of chemical identifiers CID0s and CID1s. The CID0s are individual compounds, CID1s are the merged compounds. The number being referred to is the number after CID0 or CID1. CID171549452 is thus the merged compound represented by compound 71549452 in PubChem.

In the coming version of STITCH we will change the CID0/CID1 terminology with CIDs/CIDm, where `s` is single compounds and `m` is merged compounds.