replaced apply-style proof for instance Multiset :: plus_ac0 by recommended Isar proof style
consts comp :: ('a,'v) expr => (('a,'v) instr) list
primrec
"comp (Cex v) = [Const v]"
"comp (Vex a) = [Load a]"
"comp (Bex f e1 e2) = (comp e2) @ (comp e1) @ [Apply f]"