proc nonrec find([*] int A; word top; int n) bool:
    word i;
    bool found;
    i := 0;
    found := false;
    while i < top and not found do
        found := A[i] = n;
        i := i + 1
    od;
    found
corp

proc nonrec gen_next([*] int A; word n) int:
    int add, sub;
    add := A[n-1] + n;
    sub := A[n-1] - n;
    A[n] :=
        if sub > 0 and not find(A, n, sub)
            then sub
            else add
        fi;
    A[n]
corp

proc nonrec main() void:
    [30] int A;
    word i;

    A[0] := 0;
    write("First 15 items:  0");
    for i from 1 upto 14 do write(gen_next(A, i):3) od;
    writeln();

    while not find(A, i, gen_next(A, i)) do i := i + 1 od;
    writeln("First repeated item: A(", i:2, ") = ", A[i]:2)
corp