letter$1=\text{'}$a$\text{'}$

while letter$1<\text{'}$c$\text{'}$:

letter$2=\text{'}$t$\text{'}$

while letter$2<=\text{'}$u$\text{'}$:

print$($f$\text{'}\{$letter$1\}\{$letter$2\}\text{'})$

letter$2=$ chr$($ord$($letter$2)+1)$

letter$1=$ chr$($ord$($letter$1)+1)$