This format was used by the Programming Data Facility PDF application produced by the UK Atomic Energy Authority. Below is a an example of a PDF format structure file :-
0 04-Dec-01 PDF V2.10 FIBONACCI 1, 7, 7, 1
0 Fibonacci SEQ NORM
0 - Initialis e SEQ NORM
0 1 LEAF NORM
2 Calculate SEQ NORM
0 2 LEAF NORM
1 DETAILS-3 ITER NORM
0 - Iteration _1 SEQ NORM
-2 i < 32
0 3, 5 LEAF NORM
4 Display SEQ NORM
0 4 LEAF NORM
1 DETAILS-5 ITER NORM
0 - Iteration _2 SEQ NORM
-2 i < 32
0 6, 5 LEAF NORM
-1 Fibonacci SEQ NORM
int fib[32];
int i;
1 fib[0] = 0;
fib[1] = 1;
2 i = 2;
3 fib[i] = fib[i-1] + fib[i-2];
4 i = 0;
5 i++;
6 // Print each number and its Fibonacci product
printf("%3d %6d\n", i, fib[i]);