While nosing around nearby stuff I noticed

	(* 0 1.0)  => 0
	(* 0 1+1i) => 0
but
	(* 1.0  0) => 0.0
	(* 1+1i 0) => 0.0

which seems a bit inconsistent.  R5RS "Exactness" reads like either
exact or inexact is permitted, but I imagine it ought to be the same
whichever way around you write the args.  I think I'll change the
latter two to exact 0.