#
Pascal's triangle
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The following pattern of numbers is called Pascal's triangle.

```
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
...
```

The numbers at the edge of the triangle are all 1, and each number inside the triangle is the sum of the two numbers above it. Write a procedure that computes elements of Pascal's triangle by means of a recursive process.

```
(check-equal? (solution 1 1) 1)
(check-equal? (solution 3 2) 2)
(check-equal? (solution 4 3) 3)
(check-equal? (solution 5 2) 4)
(check-equal? (solution 5 3) 6)
```