Explanation: Permission MUST be obtained when using...

[Riazuddin]

Please explain the following sentence:

"Permission MUST be obtained when using outside sources"

Why can'nt we say:

"Permission MUST be obtained when we are using outside sources"

Please define the complete structure of the above sentence in details.

thanks

[Tom]

[Riazuddin]

Thank you for your reply.

it is for the first time I am encountering the world
called ellipsis in English. I will appreciate if you could kindly provide me more details on the use of ellipsis...

thanks once again