Move paper references to end

Author: Scott Schneider

README.md

@@ -12,29 +12,37 @@ algorithms.
 The algorithmic complexity of the algorithms is with respect to the size of the
 window.
 
-A [tutorial](https://dl.acm.org/doi/abs/10.1145/3093742.3095107) and 
-[encyclopedia](http://hirzels.com/martin/papers/encyc18-sliding-window.pdf)
-article provide more background on sliding window aggregation algorithms.
+A [tutorial][swag_tutorial] and [encyclopedia][swag_encyclopedia] article
+provide more background on sliding window aggregation algorithms.
 
 ## FIFO Algorithms
 - [DABA](cpp/src/DABA.hpp) and [DABA Lite](cpp/src/DABALite.hpp) are worst-case 
-  O(1). The reference paper for DABA is [Low-Latency Sliding-Window Aggregation in Worst-Case Constant Time](https://dl.acm.org/doi/abs/10.1145/3093742.3093925).
+  O(1). The reference paper for DABA is
+  [Low-Latency Sliding-Window Aggregation in Worst-Case Constant Time][debs2017].
 - [FlatFIT](cpp/src/FlatFIT.hpp) and [DynamicFlatFIT](cpp/src/DynamicFlatFIT.hpp) 
   are average-case O(1) and worst-case O(*n*). The reference paper for FlatFIT is 
-  [FlatFIT: Accelerated Incremental Sliding-Window Aggregation For Real-Time Analytics](https://dl.acm.org/doi/abs/10.1145/3085504.3085509).
+  [FlatFIT: Accelerated Incremental Sliding-Window Aggregation For Real-Time Analytics][ssdbm2017].
   Dynamic FlatFIT is an adaptation of FlatFIT that allows window resizing.
 - [IOA](cpp/src/OkasakisQueue.hpp) is the Imperative Okasaki Aggregator and it is 
   worst-case O(1). It is based on Chris Okasaki's real time queues. The reference 
-  paper for IOA is [Low-Latency Sliding-Window Aggregation in Worst-Case Constant Time](https://dl.acm.org/doi/abs/10.1145/3093742.3093925).
+  paper for IOA is [Low-Latency Sliding-Window Aggregation in Worst-Case Constant Time][debs2017].
 - [Two-Stacks](cpp/src/TwoStacks.hpp) and [Two-Stacks Lite](cpp/src/TwoStacksLite.hpp)
   are average-case O(1) and worst-case O(*n*). Two-Stacks was originally described by 
-  [Jon Skeet on Stack Overflow](https://stackoverflow.com/questions/685060/design-a-stack-such-that-getminimum-should-be-o1).
+  [Jon Skeet on Stack Overflow][skeet2009].
 
 ## General Algorithms
 - [FiBA](cpp/src/FiBA.hpp) is the Finger B-Tree Aggregator and it is 
   average-case O(log *d*) where *d* is the distance the newly arrived item is from 
   being in-order, and worst-case O(log *n*). For in-order data, this reduces to 
   average-case O(1) and worst-case O(log *n*). The reference paper for FiBA is 
-  [Optimal and General Out-of-Order Sliding-Window Aggregation](http://www.vldb.org/pvldb/vol12/p1167-tangwongsan.pdf).
+  [Optimal and General Out-of-Order Sliding-Window Aggregation][vldb2019].
 - [Reactive](cpp/src/Reactive.hpp) is worst-case O(log *n*). The reference paper is 
-  [General Incremental Sliding-Window Aggregation](http://www.vldb.org/pvldb/vol8/p702-tangwongsan.pdf).
+  [General Incremental Sliding-Window Aggregation][vldb2015].
+
+[swag_tutorial]: https://dl.acm.org/doi/abs/10.1145/3093742.3095107
+[swag_encyclopedia]: http://hirzels.com/martin/papers/encyc18-sliding-window.pdf
+[debs2017]: https://dl.acm.org/doi/abs/10.1145/3093742.3093925
+[ssdbm2017]: https://dl.acm.org/doi/abs/10.1145/3085504.3085509
+[skeet2009]: https://stackoverflow.com/questions/685060/design-a-stack-such-that-getminimum-should-be-o1
+[vldb2019]: http://www.vldb.org/pvldb/vol12/p1167-tangwongsan.pdf
+[vldb2015]: http://www.vldb.org/pvldb/vol8/p702-tangwongsan.pdf