The standard way when using ordinal arithmetic is:
Take the ordinal 1, which is {{}}.
Replace each element with a ordered pair of the form {{a},{a,b}} with second element being 0 (that is {}).
Repeat with second element 1.
Take a union.
Take find the ordinal with this order.
Overall:
otp({
{{{}},{{},{}}},
{{{}},{{},{{}}}}
})
Or simplified
The standard way when using ordinal arithmetic is: Take the ordinal 1, which is {{}}. Replace each element with a ordered pair of the form {{a},{a,b}} with second element being 0 (that is {}). Repeat with second element 1. Take a union. Take find the ordinal with this order. Overall: otp({ {{{}},{{},{}}}, {{{}},{{},{{}}}} }) Or simplified
otp({ {{{}}}, {{{}},{{},{{}}}} })