User blog comment:Nayuta Ito/Brainfuck challenge/@comment-5529393-20160812135913

BF(70) >= 2^^^6  +++[->>>+<+[-[>[[->+<]<[->>>+<<<]>>>[-<<+<+>>>]<-]<<-]>[-<++>]<<]<]>>.

BF(71) > Ack(2^^^6)  ++++[->>>+<+[-[>[[->+<]<[->>>+<<<]>>>[-<<+<+>>>]<-]<<-]>[-<++>]<<]<]>>.

BF(72) > Ack^2(2^^^6) ++ +++[->>>+<+[-[>[[->+<]<[->>>+<<<]>>>[-<<+<+>>>]<-]<<-]>[-<++>]<<]<]>>.

BF(73) > Ack^3(2^^^6) +++ +++[->>>+<+[-[>[[->+<]<[->>>+<<<]>>>[-<<+<+>>>]<-]<<-]>[-<++>]<<]<]>>.

BF(134) > Ack^64(2^^6) > G