| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | difficult [to-vb] [coord] | 376 |
|
| 2 | difficult [verb] and | 287 |
|
| 3 | difficult [verb] but | 51 |
|
| 4 | difficult [verb] or | 38 |
|
| 5 | difficult to understand [coord] | 20 |
|
| 6 | difficult understand [coord] | 20 |
|
| 7 | difficult define [coord] | 15 |
|
| 8 | difficult to define [coord] | 15 |
|
| 9 | difficult obtain [coord] | 11 |
|
| 10 | difficult to obtain [coord] | 11 |
|
| 11 | difficult to achieve [coord] | 10 |
|
| 12 | difficult achieve [coord] | 10 |
|
| 13 | difficult find [coord] | 9 |
|
| 14 | difficult to find [coord] | 9 |
|
| 15 | difficult to measure [coord] | 8 |
|
| 16 | difficult measure [coord] | 8 |
|
| 17 | difficult to control [coord] | 7 |
|
| 18 | difficult control [coord] | 7 |
|
| 19 | difficult establish [coord] | 6 |
|
| 20 | difficult to establish [coord] | 6 |
|
| 21 | difficult to apply [coord] | 5 |
|
| 22 | difficult to predict [coord] | 5 |
|
| 23 | difficult quantify [coord] | 5 |
|
| 24 | difficult apply [coord] | 5 |
|
| 25 | difficult to quantify [coord] | 5 |
|
| 26 | difficult predict [coord] | 5 |
|
