def
  ackermann( 0, n ) = n + 1
  ackermann( m, 0 ) = ackermann( m - 1, 1 )
  ackermann( m, n ) = ackermann( m - 1, ackermann(m, n - 1) )

for m <- 0..3, n <- 0..4
  printf( 'Ackermann( %d, %d ) = %d\n', m, n, ackermann(m, n) )