Pascal's triangle

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.

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