Warm absorbers in X-rays (WAX), a comprehensive high resolution grating spectral study of a sample of Seyfert galaxies: I. A global view and frequency of occurrence of warm absorbers - Sibasish Laha; Matteo Guainazzi; Gulab C. Dewangan; Susmita Chakravorty; Ajit K. Kembhavi (Monthly Notices of the Royal Astronomical Society, 2014)