The study of heavy quarks pair production at the LHeC and FCC-eh in the collinear generalized double asymptotic scaling (DAS) approachE. Karampur and G. R. BorounEur. Phys. J. Plus, 139 2 (2024) 151DOI: https://doi.org/10.1140/epjp/s13360-024-04907-8