dileep,
i find apply1 (expr, r1); works OK but apply (apply1, [expr, r1]); does not.
looks to me like maxima is simplifying the nested sum into a product of sums
so the rule doesn't apply anymore.
not sure why that doesn't happen with apply1 (expr, r1); .
i don't know of a way to stop maxima from simplifying the nested sum.
anyway if the set of rules is known ahead of time, why not just call
apply1 (expr, r1) .
robert