fidelity remind reader of "Tr"

[wblangdon]

URL to the relevant course

Perhaps remind the novice reader what the symbol "Tr" means in
https://quantum.cloud.ibm.com/learning/en/courses/general-formulation-of-quantum-information/purifications-and-fidelity/fidelity

Select all that apply

• new content request
• typo
• code bug
• out-of-date content
• broken link
• other

Describe the fix or the content request.

def of fidelity is hard to understand

For new content requests - if the request is accepted, do you want to write the content?

(No answer)