Is it permissible to pray by gesturing when it's impossible to find a place to pray or when it's not possible to interrupt a lesson to perform it?

Standing, bowing (Ruku'), and prostrating (Sujud) are pillars of prayer that are not waived except in cases of genuine inability to perform them, such as in the case of a sick person. If a worshipper is unable to stand, it is permissible for him to pray sitting. If he is unable to perform Ruku' and Sujud, he should gesture for them, making the gesture for Sujud lower than that for Ruku'. However, studying is not an excuse to omit these pillars.