I couldn't see a ```next:completed:error``` indentation in the guidelines, when they have been chained on top of a Signal, so I'm indenting in a similar way to the [zip spec](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/master/ReactiveCocoaFramework/ReactiveCocoaTests/RACSignalSpec.m#L2500)

```objective-c
[[RACSignal zip:@[ a, b, c ] reduce:^(NSNumber *a, NSNumber *b, NSNumber *c) {
	return [NSString stringWithFormat:@"%@%@%@", a, b, c];
}] subscribeNext:^(id x) {
	[receivedValues addObject:x];
} error:^(NSError *error) {
	receivedError = error;
} completed:^{
	hasCompleted = YES;
}];
```