move int::ring_div instance upward, simplify several proofs
#!/usr/bin/env bash## psbooklet - rearrange pages of ps file to be printed as booklet (duplex)psbook "$@" | \ pstops '4:0L@.7(21cm,0cm)+1L@.7(21cm,14.85cm),3R@.7(0cm,14.85cm)+2R@.7(0cm,29.7cm)'