What would you understand by the term 'els' used in. $$B_1, B_2 \textrm{ els} Q(z).$$ The context is differential algebra and the Risch integration algorithm. My best guess is 'elementary elements of' but it's not clear in his 1969 paper. Found here: http://www.cs.ru.nl/~freek/courses/mfocs-2012/risch/1995313.pdf
Thanks