diff --git a/docs/efficiency.md b/docs/efficiency.md
index 729f83533742900b220708ff58f718c54f9a3691..9a05899047e95829a9531d8119209cdf4df48502 100644
--- a/docs/efficiency.md
+++ b/docs/efficiency.md
@@ -8,35 +8,19 @@ The basic measure of efficiency of a pairwise test generation tool is the number
 
 Test generation efficiency is one aspect of a tool that a user will want to consider when choosing a tool to use, but numbers are easier to compare than less tangile aspects like "usability", so a standard set of benchmarks emerged over the years. The table below summarizes efficiencies for several tools that happened to publish their numbers.  
 
-| # | Model | 3⁴ | 3¹³ | 4¹⁵ 3¹⁷ 2²⁹ | 4¹ 3³⁹ 2³⁵ | 2¹⁰⁰ | 10²⁰ |
-| :---- | :----: | ----: | ----: | ----: | ----: | ----: | ----: | 
-| 1 | AETG  | 9 | 15 | 41 | 28 | 10 | 180 |
-| 2 | IPO  | 9 | 17 | 34 | 26 | 15 | 212 |
-| 3 | TConfig  | 9 | 15 | 40 | 30 | 14 | 231 |
-| 4 | CTS  | 9 | 15 | 39 | 29 | 10 | 210 |
-| 5 | Jenny  | 11 | 18 | 38 | 28 | 16 | 193 |
-| 6 | TestCover  | 9 | 15 | 29 | 21 | 10 | 181 |
-| 7 | DDA  | ? | 18 | 35 | 27 | 15 | 201 |
-| 8 | AllPairs [McDowell]  | 9 | 17 | 34 | 26 | 14 | 197 |
-| 9 | PICT | 9 | 18 | 37 | 27 | 15 | 210 |
-| 10 | EXACT | 9 | 15 | ? | 21 | 10 | ? |
-| 11 | IPO-s  | 9 | 17 | 32 | 23 | 10 | 220 |
-| 12 | ecFeed  | 10 | 19 | 37 | 28 | 16 | 203 |
-| 13 | JCUnit  | 10 | 23 | 49 | 33 | 18 | 245 |
-| 14 | CoverTable  | 9 | 17 | 34 | 26 | 12 | 195 |
-
-### Sources
-1. Y. Lei and K. C. Tai [In-parameter-order: a test generation strategy for pairwise testing](http://www-cse.uta.edu/~ylei/paper/hase.pdf), p. 8.
-2. K. C. Tai and Y. Lei [A Test Generation Strategy for Pairwise Testing](http://ranger.uta.edu/~ylei/paper/ipo-tse.pdf) p. 2.
-3. A. W. Williams [Determination of Test Configurations for Pair-wise Interaction Coverage](http://www.site.uottawa.ca/~awilliam/papers/Testcom2000.pdf), p. 15.
-4. A. Hartman and L. Raskin [Problems and Algorithms for Covering Arrays](http://www.haifa.il.ibm.com/projects/verification/mdt/papers/AlgorithmsForCoveringArraysPublication191203.pdf), p. 11.
-5. Supplied by Bob Jenkins.
-6. Supplied by George Sherwood.
-7. C. J. Colbourn, M. B. Cohen, R. C. Turban [A Deterministic Density Algorithm for Pairwise Interaction Coverage](http://www.public.asu.edu/~rturban/dda.pdf), p. 6.
-8. Supplied by Bob Jenkins.
-9. Supplied by Jacek Czerwonka.
-10. J. Yan, J. Zhang [Backtracking Algorithms and Search Heuristics to Generate Test Suites for Combinatorial Testing](http://doi.ieeecomputersociety.org/10.1109/COMPSAC.2006.33), p. 8.
-11. A. Calvagna, A. Gargantini [IPO-s: Incremental Generation of Combinatorial Interaction Test Data Based on Symmetries of Covering Arrays](http://www2.computer.org/portal/web/csdl/doi/10.1109/ICSTW.2009.7), p. 17.
-12. Supplied by Patryk Chamuczynski.
-13. Supplied by Hiroshi Ukai [link](https://github.com/dakusui/jcunit/blob/0.8.x-develop/src/test/java/com/github/dakusui/jcunit8/experiments/StandardFactorSpaces.java).
-14. CoverTable's [page](https://github.com/walkframe/covertable).
+| # | Model | 3⁴ | 3¹³ | 4¹⁵ 3¹⁷ 2²⁹ | 4¹ 3³⁹ 2³⁵ | 2¹⁰⁰ | 10²⁰ | Source |
+| :---- | :----: | ----: | ----: | ----: | ----: | ----: | ----: | :---- |
+| 1 | AETG  | 9 | 15 | 41 | 28 | 10 | 180 | Y. Lei and K. C. Tai [In-parameter-order: a test generation strategy for pairwise testing](http://www-cse.uta.edu/~ylei/paper/hase.pdf), p. 8. |
+| 2 | IPO  | 9 | 17 | 34 | 26 | 15 | 212 | K. C. Tai and Y. Lei [A Test Generation Strategy for Pairwise Testing](http://ranger.uta.edu/~ylei/paper/ipo-tse.pdf) p. 2. |
+| 3 | TConfig  | 9 | 15 | 40 | 30 | 14 | 231 | A. W. Williams [Determination of Test Configurations for Pair-wise Interaction Coverage](http://www.site.uottawa.ca/~awilliam/papers/Testcom2000.pdf), p. 15. |
+| 4 | CTS  | 9 | 15 | 39 | 29 | 10 | 210 | A. Hartman and L. Raskin [Problems and Algorithms for Covering Arrays](http://www.haifa.il.ibm.com/projects/verification/mdt/papers/AlgorithmsForCoveringArraysPublication191203.pdf), p. 11. |
+| 5 | Jenny  | 11 | 18 | 38 | 28 | 16 | 193 | Supplied by Bob Jenkins. |
+| 6 | TestCover  | 9 | 15 | 29 | 21 | 10 | 181 | Supplied by George Sherwood. |
+| 7 | DDA  | ? | 18 | 35 | 27 | 15 | 201 | C. J. Colbourn, M. B. Cohen, R. C. Turban [A Deterministic Density Algorithm for Pairwise Interaction Coverage](http://www.public.asu.edu/~rturban/dda.pdf), p. 6. |
+| 8 | AllPairs [McDowell]  | 9 | 17 | 34 | 26 | 14 | 197 | Supplied by Bob Jenkins. |
+| 9 | PICT | 9 | 18 | 37 | 27 | 15 | 210 | Supplied by Jacek Czerwonka. |
+| 10 | EXACT | 9 | 15 | ? | 21 | 10 | ? | J. Yan, J. Zhang [Backtracking Algorithms and Search Heuristics to Generate Test Suites for Combinatorial Testing](http://doi.ieeecomputersociety.org/10.1109/COMPSAC.2006.33), p. 8. |
+| 11 | IPO-s  | 9 | 17 | 32 | 23 | 10 | 220 | A. Calvagna, A. Gargantini [IPO-s: Incremental Generation of Combinatorial Interaction Test Data Based on Symmetries of Covering Arrays](http://www2.computer.org/portal/web/csdl/doi/10.1109/ICSTW.2009.7), p. 17. |
+| 12 | ecFeed  | 10 | 19 | 37 | 28 | 16 | 203 | Supplied by Patryk Chamuczynski. |
+| 13 | JCUnit  | 10 | 23 | 49 | 33 | 18 | 245 | Supplied by Hiroshi Ukai [link](https://github.com/dakusui/jcunit/blob/0.8.x-develop/src/test/java/com/github/dakusui/jcunit8/experiments/StandardFactorSpaces.java). |
+| 14 | CoverTable  | 9 | 17 | 34 | 26 | 12 | 195 | CoverTable's [webpage](https://github.com/walkframe/covertable). |