Consider the following loop: for k := 0 to 3 do for k := k to k +3 do S: A[k ,k -k ] := A[k -1,k -k ]+A[k ,k -k -1]
for k := 0 to 3 do for k := k to k +3 do S: A[k ,k -k ] := A[k -1,k -k ]+A[k ,k -k -1]
for k := k to k +3 do
S: A[k ,k -k ] := A[k -1,k -k ]+A[k ,k -k -1]