op.staticAnalysis(dynEnv.getStaticContext(), sum, toadd);
sum = (XNumber) op.eval(dynEnv, sum, toadd);
}
final DivOp op = new DivOp();
final XInteger divby = XInteger.valueOf(size);
op.staticAnalysis(dynEnv.getStaticContext(), sum, divby);
return op.eval(dynEnv, sum, divby);
} else if(firstItem instanceof DurationValue) {
// Duration values must either all be xdt:yearMonthDuration values
// or must all be xdt:dayTimeDuration values.
DurationValue sum = (DurationValue) firstItem;