proofmode; calltrace;
subroutine s(index i)(var d):
x(i)=yi=d; x(i-10)=y(i-10)=d-10; cpen; 5 draw i; 10 draw i-10.
subroutine t(index i):
call `a s((i+100),100); call `b s(200,200).
call `c t(300);
.
end