shift : {d} (fin d, d >=1) => [d] -> Bit -> [d]
shift fill bit = fills
	where
          fills = [bit]#(take fill)

shift_alt : {d} (fin d, d >=1) => [d] -> Bit -> [d]
shift_alt fill bit = fills
	where
	  fills = [bit]#(drop`{1} (fill >> 1))

infZero : [inf]Bit
infZero = [False] # infZero

property shift_eq a b c d e = shift (take`{10} ([a,b,c,d]#infZero)) e
                           == shift_alt (take`{10} ([a,b,c,d]#infZero)) e