It's generally forbidden to submit the same paper at two different venues at the same time. In addition, many computer science conferences have two different submission deadlines: a deadline for the submission of abstracts, followed by another deadline (1-2 weeks later) for the submission of full papers. A complete submission consists of an abstract and the accompanying paper.
Let's say we have a situation that involves two conferences, A and B:
- Conference A had its abstract and paper submission deadlines some time in October. A's website says that acceptance notifications will be sent to the authors on December 7.
- Conference B has its abstract submission deadline on December 1 and its paper submission deadline on December 8.
Is it OK to submit a paper to A and an abstract to B simultaneously, cancelling the submission to B in case the paper is accepted at A?
(It surely seems advisable to ask the conference chair of B, but since I know the chair of B personally, I don't feel comfortable asking, since this might come off as a request for favouritism.)